I've done three of the private/personalized tours, with 3 different guys. Each experience was different. It's a big lake, and things like time of day and weather conditions can have a big impact on what the photographic potential will be. It's not an easy place to take pictures IMHO, but it's a really neat lake and I'm sure you'll enjoy your tour.
For best results you'll want to shoot at sunrise or sunset. Midday it's going to be tough to get decent photographs, although I suppose if it's overcast you might get some good stuff back in the small areas where the trees are denser. Since you're shooting hand-held from a boat, IS/VR is highly recommended if you have it, especially during the early/late light.
If you go for the sunrise tour, dress warmer than you think you need to. It will be much cooler out on the lake than on land, especially before the sun comes up. My first tour was a sunrise in late Nov when the temps were in the 30's before the sun came up, and I froze my butt off.
Here are the guides I've used, if anybody knows of another chime in.
http://paulkeithphoto.com/ - He doesn't explicitly list photo tours on his website right now, just fishing tours, so I'm not sure if he's still interested in doing photo tours. He had a speed boat, and we were able to cover quite a bit of area. He's a pretty experienced photographer, and was knowledgeable on when and where to go from a photographer's perspective.
http://www.caddolakephotography.com/ - This is John Winn, Dan already mentioned his website. His boat is docked at a different location from the Uncertain marina, and his tour will be more along the back-channels rather than out on the main lake. A very different experience, but definitely worthwhile.
http://www.oldportcaddo.com/ - These folks operate the pier and trading post in the state park. They do group tours, but if you give them a call you can also arrange a private tour at sunrise or sunset. I went out with Robert. He also has a smaller boat, but it's docked at the Uncertain marina and he can take you out on the main part of the lake.