I have dealt with this as well. 9.5.1 is supposed to be the fix for the MAS plug in in High Sierra, but it ain't.
I deleted the MAS pref "Audio Unit Info Cache 64-bit" from the User-Library-Preferences-com.motu.MotuAudioSystem folder
And
"MOTU Audio System Prefs" from the User-Library-Preferences-com.motu.DigitalPerformer folder
This forced DP to reexamine all the AU units as well as the MAS plugins, and the VePro MAS worked.
But then I closed and reopened the file and it reported the plugin missing. It still showed the plugin in the add instrument menu, but then reported a MAS error when opening.
SO
It ain't fixed.