I do music with many different "communities" of musicians in my area. Mostly tunes and songs from the southern mountains of the US. Mostly at private parties in the winter and campground jams at festivals in the summer.

For the hardest of the "hard core" old time musicians, the twain rarely meet. If you want to sing at a party attended predominantly by such, the standard procedure is for someone to secure a location, preferably sonically isolated to some extent, and then pass the word that the singers should gather at that location. There might be several tune jams at such an event, but only rarely more than one song jam. That's not to say that there are never any songs done in the tune jams. It's just that they are the occasional exception. Song junkies (like me) will spend all their time in the song jam, while those with more modest singing needs will come and go.

As we move away from the hard core old time end of the spectrum and towards the "folkie" end things change a bit. People who are not as obsessed with old time music seem to be more willing to mix their metaphors in a jam. At gatherings of these types there's more likely to be a single jam where songs and tunes share more or less equal billing.