This was something I was wondering once, and I think that the 3151 (the one that uses the same connector) was designed to be an IBM answer to the DEC VT 100 and later. I'm not really sure if they are compatible though, and I doubt they are.
The best thing you could do in this situation is to try and get an old IBM 3151/3161 or similar terminal and connect it to your DEC. I assume that this is one of those Microvaxen that's just a small box that you connect your VT220/320 to?