Surely any EASA rated TRE could sign a licence that seems crazy! I am not entirely sure it is common practice, I have worked for European Airlines and never been asked to change my UK ATPL, my LPCs were also signed off by non UK TREs. Any way I agree the system seems crazy, could you get a U.K. Licence as well as your Irish one?
I am also not that convinced that VS will be recruiting "significantly" more than 10 DEPs this year but I could be wrong. To me Virgin used to be an aspirational airline somewhere you would dream of working, somewhere where all those years of flying and all those thousands of hours actually meant something an Airline that actively wanted and sort experienced pilots. It just saddens me that it's not the case anymore, you can now just start your career right at the top. It basically says to me that Virgin value experience in the same way every other airline does, an unwanted expense.
Anyway best of luck I hope you get in at some point.