Traditionally in jazz, the bassist provides the pulse, and the drummer provides color. This isn't true in all genres. And in a bigger band, the rhythm section (piano, bass, drums, guitar) has to function as a cohesive unit.

Although, optimally, the tempo just seems to sustain itself, a condition that's only met by the best players. Playing bass alongside a drummer with great time is certainly a better experience, and there are drummers with better time than me. Time is one of those things that's a lifelong pursuit, not something that is ever "good enough." Likewise intonation.

Using Jamulus, it seems to work best when the tempo is driven by instruments that can be isolated from the feed coming from the headphones, so for instance electric bass works better than double bass, though they both function as "bass."

I think he means that in this case it’s a mistake as it would be wisest to take the tempo from the electronic instruments.