We had some old, unimproved bahia on the farm I grew up on, down in east-central AL... pretty low productivity; unless the newer selections are a whole lot better, I'd hazard a guess that crabgrass would whip the heck out of it as a summer forage source.
I looked up the normal range of bahia grass and the map didnt show very much of TN included, so I would think you might be too far north. Down here below the fescue belt I like bahia over crabgrass, because the bahia will grow into the fall better than crabgrass, up there I would think your fescue would cover you in the fall when the crabgrass stops growing. Grass is so much about where you live, ask your extension agent for help..
Several years back, I was actually looking around for a source for dallisgrass seed to add to the sward here for more warm-season grazing. Was noticing a couple of nice patches of it on the side of the highway on the way home, and even considered stopping and hand-harvesting some seed.
Then... all of a sudden, BAM! it appeared in the pastures. It was Everywhere. Don't know how long it'll stay before taking a hiatus, but it's come back every summer since. No major problems with ergot, so far.
About a 1/3 of our best ground was the most beautiful stand of Dallis last year. Hoping its here every year. That stuff grows a ridiculous amount, and quick.
Lucky_P - I think i'm crazy for it, but I have about 3 gallon bags in the freezer. Stuffed full with Johnson Grass seed. 50% of the time I think I should throw it down. 50% of the time I think i am insane. Which I probably am just insane.
Both Johnson and Dallas grasses are prolific down here but do not like a lot of pressure. Thinking about it, places where I had both and were undesirable, constant mowing pretty much did away with them.
In the hay patch, no Dallas there to start with but the JG thrives since it's a rhizome spreader. It excels with the plow. If it keeps spreading like it is, In a few years I may quit buying sorghum sudan seed and just cultivate JG.
Dallas can get some sort of fungus on the seed heads. If you have it you can recognize it in the heads. Check with your ag. extension folks. I have grazed it and baled it and never had a problem but like prussic acid possibilities with JG and sorghums, there is always something to bite you in the butt!
I have baled and fed JG to horses and had no problems. Some say don't. Sorghum sudan seed mfgrs. say don't. Agree that cows love it. A lot of people call it a weed. Definition of a weed is something undesirable in your undertaking, not necessarily a derogatory term.