For someone getting sub 20mins now, looks like Dallas has solidified Lively as their clear no.1 center option. So moving afford for some depth and a bit of draft capital could be a good move for them.
Jock and Tate are probably too good to be 3rd options on a team, but because of Houston's depth (Sengun and Adams being ahead of Jock and, Amen, Tari, Bari, Brooks being ahead of Tate) haven't had enough playing time.
That said, Gafford would move ahead of Adams as the backup 5, which helps with Adams still recovering from nagging injuries.
Jock would play a different role at the 5 than Gafford and would offer a more dynamic lineup with his shooting (which is.. ok? For a big). Tate will be another body to throw at wing defenders and is an absolute dog.