If you go all the way to the bottom of the page here ->
https://disneyworld.disney.go.com/guest-services/photo-pass-service/ you can see maps of where they will typically staff photographers. There aren't on ride photos like there are on ToT & SM, but often times they will hang out in the bottom of rides like Teamboat Springs to take a group shot of you in the raft before unload. You can carry a waterproof camera with you on most slides (not 100% sure on all slides). It really depends on what you want pictures of. A few to show you were there and did the rides, then MM should be sufficient. If you want shots of them on the lazy river, in line for slides, etc then you would want to bring your own camera of some sort. Keep in mind they only staff photographers at the water parks seasonally, and there is a chance if the weather is iffy they won't be there.