In theory, you should be able to configure a VPN tunnel between these two. They both say that they support site to site VPN tunnels, IPSEC, and and IKE. Thus, if they really support the standards it *should* just work.
However, from experience, configuring something like this can be a real pain. If it were me, I would just press to find a way to get the same device on each side because of all the unknown issues and time associated with trying to make it work. but that is just my opinion.
Best of luck to you,