I would like to record a chord progression in a looper and then jam to that in a public session. It would be great for others to join in as the chord progression plays on the looper. Is using a looper considered proper Jammr etiquette? If I don't use the looper then all I can do is play the chord progression continuously while others jam, or I can join some other session and jam to their chord progression.
The short answer is: yes, loopers are fine! Use loopers to support the jam and leave space for others to play.
I use a looper when there are not enough people to play the chord progression. For example, if there is one guitar, bass, and drums then it can be nice to have a rhythm guitar loop playing the chord progression.
Since all levels of musicians play together on jammr sometimes there is no one except you that can keep the chord progression going (playing a chord progression to the beat requires skill that is often overlooked!). In that case a looper can allow you to play a solo before returning to playing the chord progression again later.
If your looper has a tempo (BPM) setting and a quantize feature then it's easy to sync it to jammr. If not, then you might find it's hard to keep the loop from drifting away from jammr's metronome.