Vanos is not the problem, the DME handles it so don't worry. The only reason that going the M50 route is so common is because of the EWS system. It disables your ignition and your fuel if the the computer doesn't recieve the green light from your EWS module that the car isn't being stolen. Because M50s were only produced in OBD 1 form, the only thing you have to do for them is get a red label DME.
Basically it goes like this. There is a chip in your key with a specific code in it. When the key is put in the ignition, an antenna picks up that code and sends it through transfer module to the EWS module. The EWS module processes that code and tells the DME its okay to start.
If you want to use the M52, you have two options. Convert it to OBD 1 by using OBD 1 sensors and intake manifold or 2. transfer the ews system from the 328 and find a way to make it look proper inside your e30. This will also result ina dual key setup, one to crank the car and one to disable EWS. To do the latter you will need to read up on the EWS and figure out which wires need to be kept and connected and which do not. There are guides out there, just look deep. The benefits are 10 fold in that the full potential of your motor is there thanks to VANOS (aka 200 lb/ft of torque instead of 120) and you have a factory security immobiliser to protect your baby)
This page should help you out, look at the diagram
Theres also writeups out there where people have listed the pinouts that you need for the engine harness adaptor including EWS