I can confirm we did that in October '18. Seaborne actually moved the flight up an hour cutting our layover time to 32 minutes. We got off Jet Blue Flight and found Seaborne had moved their gate closer than D and it was actually just on the other side of SJU Margaritaville (maybe B?). Our walk was 5 minutes and we got on and they were at the gate for at least 15 minutes until departure (we boarded plane so couldn't see after that).

No checked bags....

Even IC people were at gate in Feb up until we boarded...