There have been many successful ports from IBM mainframe to LUW. No idea how many were VSE.
Search these forums for “rehost”. Then search SAG-L, the listserv hosted by the University of Arkansas.
Porting Adabas files is easy (unless your users won’t accept ASCII collating sequence or you mix packed values into your alpha fields). It just takes a bit of work. Adabas provides all the utilities you need. 99% of your Natural code will move cleanly, but there are a few syntax incompatibilities, a few coding techniques that are problematic, and ASCII conversion.
Getting help can be difficult because those with the most experience in this area (independent contractors and SAG professional services) hesitate to give this advice for free.