When a magus (including a Redcap) of the Order is a guest at a covenant (e.g. taking advantage of the three days/year of hospitality that come with Redcap registration - see HoH:TL - or when attending a Tribunal), according to custom is he formally invited inside the Aegis and given a token to protect him from the magic-dampening effects of the Aegis? I would say yes, or I would see all sorts of problems arising (e.g. it would be extremely difficult for loamwalker RedCaps - from RoP:M- to function).
It would be very rude not to give such a guest a token.
Hoever, I don't think the hosting covenant is required to do so.
If there is any reason why the hosting Magi think their guest shouldn't have a token they can render it useless at any moment they like.
It happened in my troupe once, when an 'old friend' came back to the covenant. She was welcomed with all proper respect as a fellow Maga. During the less than friendly conversation two of our players withdrew her token at the same time. (that really set the tone for the rest of that game session 
)
I suppose that after see if his identity is the correct, and that there aren't any conflict the covenant should give him. But it's true that the Redcaps don't have sobrenatural powers so communly for the guest...
Well, on the other hand, the occasional Gifted Mercere does take on Redcap duties, and the occasional unGifted Redcap does have a supernatural ability... and it would be kind of rude to treat those who do not differently from other magi, somethink like stressing their "inferiority".
It is the odd quirk of my mentem maga in my current saga that our aegis tokens are knives. We give the token to visiting magi with the message when it is given out, "we trust you to be armed in our presence."
Still, I could see a defensive covenant refusing the token. A visiting mage should not necessarily need to be casting spells in the covenant. Most that they would cast could be cast just outside the aegis limits.
Note that spells cast outside the aegis are resisted by the aegis when they enter it (e.g. a spell cast by a magus on his clothes with Moon duration, e.g. to keep them clean, is resisted by the aegis when the magus enters it).
Also note that, as most familiars have Might, it is hard to visit the covenant without a token for your familiar at least. Certainly, our magi wouldn't leave their familiars outside.
Chris
Not to mention mages with Faerie/Magical Friends, Ghost Warders, Guardian Angels, immortal magi, etc.
So the question is:
Is there a custom regarding visiting magi and their escorts?
In my case the question originated from a player who wanted to play a Faerie (Mercere) Redcap, and I was not sure whether it would be a reasonable choice - in the sense that if the Redcap was not given tokens when visiting covenants, he would not be able to enter - making him not really suited to the role.
I would think that a token given to a magus would also cover his familiar. Not a ghostly warder or summoned spirit, just his familair (via their shared arcane connection).
I would suggest making a human with Strong Faerie Blood and using several points of virtues to pick up some faeries abilities/powers (either via Sympathy or by grabbing the faeries virtues made available by Strong Faerie Blood).
Chris
Well, the whole point of the exercise was trying out a faerie 
A Redcap seemed like a fun character to play as a faerie, but if we had to choose between Redcap and faerie, we'd choose faerie
Thats so cool. I love it.
I'd never considered before that an aegis would affect a mages hangers on, IMS my necromancer typically travelled with a few helpful spirits bound into items he wore, when he got casting tokens to visit other covenants i never thought that his spirits would remain blocked.
How would this work with a spirit possessing a magus, or one bound into jewellery on the magus' person? Would the jewellery refuse to enter the aegis? Would the spirit be forced out as the magus enters?
I think Parma Magica extends enough to cover clothing and jewelry. So first you'd want to check the penetration of the Aegis of the Hearth against the magus's Magic Resistance. (Of course, many HR to get rid of this penetration.)
A possessing spirit is holding itself in place via magic. I would think it would not be able to hold on tight enough. I suppose you could compare the penetration of the possession to the penetration of the Aegis.
Depending on the binding, I would expect the Aegis may be too weak to break the binding. If the binding is ritual type it usually requires a semi-specialized ritual to break it. In that case, the Aegis would probably keep the person/thing and the spirit out. If the binding is of a more temporary nature, I would expect the Aegis would act like I suggested for possession.
Chris