I've never had a chance to raid with my guild (we have no problem filling raids, sadly... ) but I've PuGged some of the easier 10 man raid content (Sarth, VoA, Maly) and always, always roll with all my characters.

I have the same consumable cost (WHY DID I ROLL HUNTERS AS THE DPS IN MY FIRST 80 TEAM?!... argh.... *cough*...sorry), the same repair bills and clearly contribute alot more to the raid than the single character members so I just wouldn't bother if my characters weren't treated as individuals.

If I did ever go on a guild run, I'd be rolling as an alt on every character anyway, which (under our rules) gives mains priority if they need an item for their main spec.

I'm comfortable with that - I want our mains geared up ahead of the rest of us.

In your position, with the GM unsure of how to handle the situation and open to suggestions, I'd say it depends what your normal guild loot rules are.

If they contain an allowance for alts rolling on loot, clearly all of your characters are entitled to that roll (because your main is a priest).

If they don't contain that sort of allowance, it's arguably a bit more tricky and I'd suggest adding that as a general improvement to the rules anyway.