Changing the meter to a compound one is merely a tempo hack. It forces the accompaniment tracks to play differently, and you still won’t get triplets in exported scores.
If you write your own MIDI importer, Hookpad 2 also supports arbitrary note / chord lengths, including triplets, and will play them properly:
Because there isn’t really editor support for them, if you copy a triplet note and paste it everywhere like in this screenshot, these would all last for 1.33333333333333 beats causing the last note to be 10-14 beat earlier than the measure mark, or if the last note aligns, a rest of the same duration would have to appear somewhere between those notes.
MIDI-based DAWs sidestep around this issue by allowing projects to define the PPQN (pulses per quarter note) value and use different grid resolutions that evenly divide the PPQN. In Hookpad this is 4, or 8 (not 12) if the beat unit is 3. All time points are rounded to the nearest multiple of the shortest duration governed by this PPQN, which Hookpad 2’s own MIDI importer already does. Since the editor now has horizontal-only zooming, it would make sense for Hookpad to support finer time resolutions and support real triplets along the way.