Yes, hybrids can breed, so a fish that is 99% roach 1 % bream can breed, just as a 50/50 roach/rudd .
so the mind boggles.
so a fish with the correct ray count can still be a "slight hybrid"
Sadly, because roach are my favourite as many other anglers, along with rudd, there is no way of telling if they are true or not. Even killing them (no don't) will not prove anything.
Just enjoy what you catch.
Keith.