A similar issue popped up in a discussion of "what exactly is Quiet or Subtle magic, and can it be used to get around the Holy Magic penalty for words/gestures?" The general response was "Virtues are just mechanics. As such, it depends on how you define those virtues in-game. If you define them as realizing that the pagan words and gestures are unnecessary, then yes. If you define it as successfully replacing the words and gestures with appropriate Holy thoughts, then yes. If you define it as internalizing the pagan words and gestures, then no. It's up to the Troupe and the player."
So that would probably work as a similar response here. If you define a partially-integrated Hermetic virtue as already having as much of the paganism stripped out as possible, then it would work just as well as any other Major virtue. But if you define it as requiring a "pagan mindset" (or whatever), or rituals that specifically counter the ideals of Holy magic, then no - it wouldn't work.
Personally, as the RAW doesn't forbid it, I'd go with the interpretation that allows the player to do what they want.
(The other fun virtue to slip in there is the Animal Sacrifice one, from HoH:TL - that allows you to substitute an animal for vis in a summoning ritual. Which would actually fit OK with mythic Judiasm...sort of. I guess. In angel summoning? I dunno. Animal sacrifice in the Old Testament really seemed to be a way of feeding the priests, as much as anything else.)
EDIT - the reason I came up with that combo is mainly because it creates a situation in which I'd actually want to play a Mercurean as a PC - with all the penalties that it implies. Specifically, the stacking of the 1/2 cost of Vis and "you can use long-term fatigue as vis in a 3-1 ratio" is interesting enough that I'd be willing to put up with all the other stuff. The disadvantage is that the restriction on spont magic collides with the Holy magic restriction on using hermetic spells.
I'd probably add in the "quick ceremony" minor virtue from HoH:S, describe it as part of the character's Mercurean training, and call it good. (Maybe with the Cautious with Concentration virtue, as well.)
EDIT II - for example, I've always interpreted Mercurean magic as being more "structurally reinforced" than traditional Hermetic magic: the words and gestures are pronounced more cleanly, with structured foot and whole-body movements that prevent the spontaneous casting of the Diedne. But as a consequence, those gestures allow vis to more efficiently flow through the magic, and thus make rituals easier and more efficient. And because it's so structured, other magi with similar training can join in more easily.