I don't think a logo on a nice black shirt is bad, maybe I would do the writing in blue or a darker color, not white, but I don't see anything wrong with it at an informal wedding. At some events I've been to as a guest, that wouldn't work, only suits for men, and formal wear for the lady photographers.
It's white on black because that's my branding; same font, same colors, etc. And I still only wear these shirts 90% of the time; I dress for the ocassion and will wear better clothing when I'm shooting a more formal affair. I have a black-tie wedding in November and will probably go in a (non-logo'ed ) tux.