since DEC tried hard to keep RSX/VMS 'finger compatible' though I have no first hand
experience with RSX to say for sure.
Hrrmpt... maybe/sort of/after a fashion ... as a UNIX guy and someone that lived it (much less an ex-DECie), I famously argued with Cutler that he didn't! [It's a good beer story for some time in person, but not really for TUHS other than to say it happened, and it was a VMS vs. UNIX debate between DC and myself one night at the old Maui Kai in Littleton, MA with our old common boss rsg (a.k.a. Fossil) acting as the referee]