Hi, as the other poster said yes you can have multible site connected through a tunnel, most document refer to the GRE tunnel which is a point to point connection, GRE tunnel do not send multicast traffic by default so routing table keep alives are not sent across, however you can configure ip pim sparse-dense mode to send multitraffic across the tunnel, see the document below.
I was tasked with setting up multible tunnels for our network using the tunnel mode gre multipoint see some sample config below.
tunnel 1
interface tunnel0
ip address 2.222.254.111 255.255.255.0
no ip redirects
ip nhrp map 2.222.254.1 10.10.222.22
ip nhrp network-id 10
tunnel source loopback0
tunnel mode gre multipoint
interface Vlan222
ip address 2.222.11.1 255.255.255.0
ip policy route-map quarantine
route-map quarantine permit 10
match interface Vlan222
set ip next-hop 2.222.254.1
xxxxxxxxxxxxxxxxxxxxxxxx
tunnel 2
interface tunnel0
ip address 2.222.254.145 255.255.255.0
no ip redirects
ip nhrp map 2.222.254.1 10.10.222.22
ip nhrp network-id 10
tunnel source loopback0
tunnel mode gre multipoint
interface Vlan222
ip address 2.222.45.1 255.255.255.0
ip policy route-map quarantine
route-map quarantine 10
match interface vlan222
set ip next-hop 2.222.254.1
GRE multicast tunnel
http://www.cisco.com/en/US/tech/tk828/technologies_configuration_example09186a00801a5aa2.shtml