The drums provide the beat but the bajo sexto emphasizes it and gives a lower pitch to the accordian's tenor lead in Tejano Conjunto music.
One of the best bajo sexto players was Oscar Tellez. Oscar has accompanied many legendary Tejano accordianists, including Steve Estaban Jordan, Flaco Jimenez and the Dancing Cowboy, Mingo Saldivar.
Incidentally, Flaco was an integral part of the Texas Tornados along with Doug Sahm, Freddie Fender, Augie Meyers, and Ernie Durawa. Oscar was a regular with this Tex-Mex supergroup. They could do it all, a fast Texas two-step or a slow belly rubber.
Sadly, Oscar died in car accident in 2002. Doug Sahm died in 1999 and Freddie Fender in 2006, excellent muscians all.
Yeah, I'm Appalachian Kentucky and tend to prefer bluegrass, but I did a fair amount of TDY to Texas in the late 80s/early 90s and came to appreciate the music down there.