Considering there are a lot of underground rock scenes, I suspect there could be the underground equivalent to manufactured boy bands and girl groups. That’s right there with choirs, be it secular (folk) or religious (church choirs) as well as busking music groups. It could be that I had relatives who were in choirs so there’s that.
It can be argued that since there are solo church and busking performances (if I’m not mistaken), they’re equivalent to pop star performances. Maybe not exactly and consistently but when pop stars do take time to record Christmas folk songs and other folk songs in general (this is more of a thing some Filipino, American and European singers do) so there’s going to be a crossover.
Underground in the sense that whilst they don’t write their own songs and play instruments, they’re not that commercial either. From my personal experience with choirs, they do have DVDs but they’re generally that un-commercial. If you look hard enough with choirs and the like, they’re practically the genesis of and underground equivalents to pop stars really.