At chargen, there are few major virtues that would not make a grog something other than a grog. (And quite a few minor ones that would, such as Supernatural Abilities. Companion-class characters have a maximum of 10 Virtues/Flaws, but there is no minimum.)
A grog can be interesting and standout without being a literal blessing to a covenant. I've seen players try to introduce "grogs" who are Second Sighted, Educated, and have Arcane Lore, can set up a Lab, Scribe at the max for their age and speak 4 languages - and the player doesn't understand why this is "not acceptable". Imo, ims, it's because that's not a "grog" - it's a low-virtue companion class character. A "grog" is a run-of-the-mill peasant, a red-shirt, a trained fighter and grunt labor specialist, nothing more. They can be good at what they do, but they shouldn't be expected to do much more.
(And I'll mention this again - in medieval society, people didn't tend to have several craft/professional skills that they were good at. They picked one and stuck to it - that's "what they do". For a grog, their Abilities define their role, their "profession" that makes them valuable. A grog might be a single-weapon type, or a cross-bow type, or a bit of both, but rarely would they be a master of all weapon forms plus a skilled tracker plus an elite bowman and brawler plus an expert Chirurgeon plus plus plus.
A peasant tends to do their best to fit one role, not (m)any. If they're a forester, then that's what they'll do well - bow, stealth, tracking, awareness maybe some spear, whatever. If a melee brawler, then that. If a scout, then skills that serve that role. They don't have the luxury of pursuing something else when that role is what puts food on the table. That is, their skills should reflect their history and past duties and grow organically from that, not chosen off some shopping list of needed skills that the covenant could use. If the covenant needs a Chirurgeon, then they should probably have to find one, and not discover that the axe murderer grog is also a master healer.
It may be fantasy, and there is certainly room for exceptions and the unexpected, but I still lean toward Roles, not Rolls, even for grogs.)
That said, I believe there is room for "other categories" of characters. If a Grog has 3 virtues, and a Companion 10, then maybe a Shield Grog would have 4, with "Custos" free. (If a grog is promoted to Custos, they certainly don't have to lose an eye or become a drunk to make up for that!) Similarly, if a grog were blessed, or found True Love or became a Lycanthrope or whatever, they might still be a "warrior" for the covenant, but their classification in the saga might be bumped to something more than a faceless, disposable redshirt.