It is possible and many texts exist that demonstrate how to interface the two simulators. You can download and check the following reference that might help you out:
Hasan, M.S.; Yu, H.; Carrington, A.; Yang, T.C., "Co-simulation of wireless networked control systems over mobile ad hoc network using SIMULINK and OPNET," Communications, IET , vol.3, no.8, pp.1297,1310, August 2009