ferris, I would guess that would depend entirely on the bakery owners themselves and what they decide. From what I've read, there are varying interpretations of the sinfulness of homosexuality depending on how binding someone considers Shariah law:
http://variety.com/2015/voices/opinion/islam-gay-marriage-beliefs-muslim-religion-1201531047/I would guess that, just as there are practicing Catholics who believe abortion is murder and would never have one themselves but are perfectly willing to sell their products to people who are pro-choice, it boils down to what's acceptable for each individual under each circumstance.
I don't see the question as a win/lose one. If I were a bakery owner who felt strongly enough about gay marriage to not want a gay couple as my customer, I'd make some excuse as to why I could not supply a cake on that day. I wouldn't frame it in the context of it being because it's a certain type of wedding. And if I were part of the gay couple, even if the bakery owner were tactless enough to say why they were refusing, I'd simply look for another bakery rather than make a Federal case (literally) out of it.
Privately owned businesses have the right to refuse service to anyone (if they're stupid enough to say that it's on the basis of someone being in a legally protected class, that's their own fault), and customers have the right to take their business elsewhere. I really don't see the logic in wanting or trying to foist one's personal religious dogma onto anyone else.