Is this an allergy issue? I simply decline any cake where there's a question of an allergy. No matter how well you clean equipment, there is always a risk of possible contamination and I just don't want to take that risk.

Yes it is...it's made from bones, cartilage and skins or pigs, cows and horse.....not very vegetarian is it!

And glycerin is also an animal product.

Yes to both, so even MMF is a "no no" for an avowed vegan. I have a SIL who is freakish about this. Even when I'm just having her for dinner, I cook all her stuff first so there is no issue of whether a knife used for meat, eggs, etc. is used for her food. She's my one and only vegan so I accommodate her (even though she's never asked me to, I just do it so she can relax and enjoy the evening.)

edited for typo

edited again to add that some say Kosher marshmallows use agar(sp?) instead of gelatin so that might me an alternative...

This might be one of those instances where you would need to do a shortening-based buttercream rather than fondant....would simply things a lot. We discussed the possiblity of marshmallow fondant made with vegan marshmallows, which are agar based, but I do not know how well they would work....maybe some on the board has tried it...I googles them and they are $$$ compared to regular ones.

Satin Ice contains glycerin...and even though it is probably a small amount, it is still and product derived from animal sources.