I'm not trying to be alarmist and I don't have RoP:Magic yet (it's on it's way but I usually receive things about 2 weeks later than most of the Berklist/forums as I live in Oz like Timothy. Sometimes I have the rare pleasure of receiving my copy before the line editor receives his in Japan but I think it's only happened once...)
AFAIK in ArM5 canon there is no sure way of telling whether a scoured spirit is Infernal or Magic or Faerie etc (perhaps a concealed roll against the various Lore skills of the character - not sure, might have to ask Erik D on that one). An Infernal spirit can easily trick most summoners that it is Faerie or Magic in nature as Hermetic magic, Faerie magic or Infernal magic is unable to discern this. Divine aligned powers can (Sense Holiness or perhaps a warning from a Guardian Angel etc).
Let's say you avoid scouring and stick to summoning spirits you have Arcane Connections for, say ghosts who have bones available. You can only summon ghosts that have not had a "proper burial" (Christian, Muslim, Jewish or yes even Pagan). There is usually a reason for the lack of a common burial / easy access to the remains - most of these reasons are linked to some kind of sinful activity on the part of the deceased or death by violence / accident etc. There is no guarantee that the ghost will be a Magical one (or a Faerie one) from just scrutinising the remains - you might get an idea that summoning the spirit of a serial murderer or usurer is likely to result in an Infernal spirit, but what about nameless ghosts etc.
You can't summon airy spirits without some form of arcane connection, which usually requires Hermetic Theurgy etc.
True Names in ArM5 canon are only available for demons and Divine creatures - a summoner can't tell these apart just by reading them even if OOC you know that if you study Divine Lore you won't be learning a demon's True Name from the way the mechanics work. In reality grimoires were scattered through with names of demons, angels and "lesser angels"/airy spirits which all gets a bit vague - see Gustav's "Dictionary of Angels" to get an idea:
amazon.com/Dictionary-Angels ... 600&sr=8-1
(incidentally this is a great book for names etc for spirits/entities - it covers most "real sources" but also draws on literature/myth and occultism so it's not that reliable but it's very good for RPG ideas)
In summary, even if you obtain an Arcane Connection to an entity you think is MAgic/Faerie, there is no guarantee in game (except by Divine aligned powers) this is not actually a link to a demon/Infernal creature.
The risk is there and alluded to in the Ars Goetia chapter IIRC.
Possibly another point, but Pagan does not necessarily mean Infernal. Pagan and associated with cthonic dieties (Hecate for example) places you at much greater risk as it's a bit unclear if she is a Magic entity that has become Infernal, always an infernal entity or whether there are multiple entities referred to as Hecate...
I think being a summoner is the risk, not being Pagan.
Not inherently fatal, but it's difficult to avoid the price...
Summoning is tainted, regardless of Realm and carries with it the risk of attracting demons.
Commanding is out and out an Infernal aligned ability, so it's a strong link to the Infernal and the risk of corruption by demons.
IMO it's young summoners that are at most risk as they have the most to gain from "taking short cuts" and may inadvertently summon spirits aligned to the Infernal Realm that they are not powerful enough or sensible enough to dismiss without compromise.
Old summoners are the ones that have avoided the temptation of a quick/easy/corrupt (ie Infernal) path to power and have carefully avoided bargaining with anything they don't know the true nature of / can't command or coerce directly without resorting to sinful powers / sacrifices etc.
I don't think you need an explanation why Ludo isn't corrupt now - he's proven he's smart enough / skilled enough / sensible enough to avoid dealing with demons.
What I think would be an interesting aspect to develop is why he didn't become corrupted by his Goetic powers, when he was still young and most at risk of temptation and folly.
The Sense Holiness idea was just an idea towards that - it's really only useful for low level entities and to a starting character as by mid career the entities summoned are too powerful to be reliably discerned and a summoner needs an alternative strategy to deal with unwanted INfernal spirits...
This is a good point - I'll concede that without a related Story Flaw, it should play a lesser role and hold any Storyguide/Troupe to that.
My point is that these powers seem to have an inbuilt "risk of damnation" built into them as a counterbalance to their IMO superior power strength compared to other abilities.
He is descended from a lineage that succumbed to corruption.
He is a Tytalus, which although not necessarily pone to sin in itself, makes it difficult to avoid sin, regardless of whether he follows Callichean or Hippian ethics - last time I checked there were no highly devout Tytalan magi depicted in any of the prior editions...
He is a pagan, which makes avoiding damnation difficult as although he is not necessarily damned by not following a monotheistic religion (he just has to follow the precepts of his Pagan faith), there is more chance of misdirection and straying from the path IMO.
It's not a big deal - it's just potentially interesting in terms of stories.
Hope that all helped - really I think he's a great concept for a character as it is and I wouldn't let anything I have to say delay you from finishing him off and jumping right into the Saga!
Which seems to be hotting up...