I have been working with setting up a Site to Site VPN and while I can get the tunnel setup and am able to ping across the tunnel. I am unable to use the DNS server from the remote side of the tunnel. I can ping the server and otherwise access via tcp/ip but if I try to use nslookup our ping it via name it will not resolve over the IPSEC configuration. I have tried adding the domain information to the PC DNS configuration and I can then ping the server by name but NSlookup is still unusable. I have also tried using the Easy VPN server / Client method on the routers. I am able to use the VPN client on a PC and initiate a connect from (the Internet) and I will get DNS information from the primary site and all is fine. But using the Router client on the other side I cannot resolve DNS over the connection. Here is a brief Config Example.
Router A - Main Site
Internal Lan - 172.16.1.x
Router B - Site B
Internal Lan - 172.16.3.x
I have been able to ping across the subnets but internal DNS resolution isn't working for me. I can post more detailed configs if necessary.
I did not answer the question about having both GRE tunnels and Easy VPN server initially because I have not done that and can not say authoritatively whether the combination works or not. My opinion is that it should work. I do not know of anything that would prevent the combination from working. Perhaps someone with experience with this or someone from Cisco can speak to this issue.