Hi,
I read the same thing about beets and lettuce. I think lettuce goes with anything. At least that is what I've read. I have beets and lettuces growing beside eachother also. The beets are coming on, as I can see the red root just above the ground and my lettuces have gone crazy. I also planted turnip greens and some onions. Evidently, the compost I used in my raised bed didn't get got enough to kill the tomato plants and now I have them all over my beet and lettuce area also. I'm not too concerned as the smell of the tomatoes might just deter something that the beets don't like. Anyway, I heard that lettuce and beets go with just about everything. I wouldn't worry too much about it. Enjoy your garden! :-)