I have not tested this particular scenario. But since Cisco IOS does allow two point to point serial interfaces to have IP addresses within the same logical subnet and since a GRE tunnel (and I am assuming that when you indicate tunnel0 and tunnel1 that they will be GRE tunnels) is a point to point link, then I assume that you would be able to configure IP addresses within the same subnet. Whether it really makes sense to do this depends on aspects of the network topology that we do not know.
HTH
Rick
HTH
Rick
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