I have a VPN 3015 used for WEBVPN connections, and an ASA 5540 used for IPSEC connections.
I use the same public IP address for both.
The VPN 3015 and the ASA 5540 are behind a PIX 525, on a DMZ.
I have done this on the PIX 525:
static (DMZ,outside) tcp public_address https local_address_for_VPN3015 https netmask 255.255.255.255 0 0
static (DMZ,outside) tcp public_address 10000 local_address_for_ASA5540 10000 netmask 255.255.255.255 0 0
static (DMZ,outside) udp public_address isakmp local_address_for_ASA5540 isakmp netmask 255.255.255.255 0 0
It works fine for the webvpn connections to the vpn3015, and it works fine for the ipsec connections to the ASA 5540 but only for IPSEC over TCP, but not for IPSEC over UDP
I think the problem is the ESP protocol.