Hi Abbas,
There is no issue in sharing the failover link for stateful. You do not even need to seperate the interfaces with subinterfaces.
something like below.
failover lan unit primary
failover lan interface failover gigabitethernet0/2
failover interface ip failover 192.168.254.1 255.255.255.0 standby 192.168.254.2
failover link failover
Hope this helps!
-KC