Yes, it is possible to run IPSec Over TCP on the routers. Please refer the information posted by Gregory in the previous post.
As far as the second part of the question, IPSec Over TCP is an option you use when you have VPN Clients connecting to the IOS Router that acting as a VPN Server. By enabling the option "IPSec Over TCP", all that you are doing is Encapsulating IKE and IPSEC packets in a TCP Packet. The packets are already encryped using ESP.
If you are looking to just tunnel traffic across two routers without encryption, then you could use GRE. But again, in GRE there is no encryption, so no confidentiality. So, if you have sensitive traffic flowing across the sites and your security policy is to provide confidentiality for that traffic, do encryption.
I hope it helps.
Regards,
Arul
