Hi
Yes you can have 2 entries under your crypto map statement ie.
crypto map vpnset 1 ispec-isakmp
crypto map vpnset 1 set peer "site 1 vpn3000 ip address"
crypto map vpnset 1 set peer "site 2 vpn3000 ip address"
...
The pix will use the 2nd site vpn 3000 if it doesn't get a response from site 1 vpn 3000.
HTH
Jon