I too was hoping to pick up the PS1 Classics for my future vita.
Does anyone know if there is a master list of what is compatible and what isn't in terms of ps1 classics for the Vita?
I found an old listing on IGN, but it doesn't look like it's been updated in over a month.
The best way is to use the Vita web store to buy the PSOne Classics. It will automatically filter out the ones that only work on the PSP. Otherwise, just double/triple check each title you are thinking of purchasing to make sure it says "PS VITA".
[Kind of off topic, but from what I've experienced so far, trying to play Gex on the Vita is a terrible idea]