Hi,
I don't foresee any issues having 2 subnets on the same LAN.
For instance, hosts on 2 different /24s will not be able to reach each other although connected on the same flat LAN. To reach the other /24, a route or default gw would be required on the hosts which is why I would have thought simple routing would be enough to route between the 2 subnets.
Cheers,
Ashvin