Ok, sorry for the late post!
This is the first successful test of ChucK -> MIDI -> my new keyboard, a Roland VA-3 that I bought from a coworker.
Everything seems to work rather smoothly. This proves that the problem in the earlier setup was not caused by ChucK or the MIDI system of my computer, but either by the loopback, VSTs, or the VST host.Â
Looking forward to exploring the cheesy options, this one has a big tone bank.