Bearing in mind their market and customer base I'd imagine there's far more risk from Scottish independence than Brexit.
Either way, this is navel gazing. Check their history, financials and customer base. True, there is likely to be a much smaller local talent pool up there, but equally I'd imagine the quality of life is something to behold. For some, that's quite a pull.
I note the CEO is based in Cambridge. But the company appears to be a couple of decades old. I doubt the CEO visits more than twice a month. The who-are-we page is otherwise finance, sales and admin people bar one. That says to me it's not very innovative, living off recurring government military contracts.
The only way to get a feel for a place like this is to go there and press the flesh.