I don't (play with a bassist). But yeah, that's exactly why I went 7-string -- because I come from a piano background, and I want as much of a range as I can handle. Eventually going to work my way up to 8 string (NS/Stick).
But also, there's this whole school of guitar playing called gypsy jazz, and yes, that's exactly what the 7th string is for -- it's for the bass back beat. Here's my favourite 7-string jazz guitarist (I don't think this is gypsy jazz, though):
And finally -- the metal players. So what happened was, they (starting with Black Sabbath) started down-tuning their guitars to sound heavier, and down-tuning some more, until they ran into issues with scale length, so finally just started playing baritones or playing 7 strings.