If you have logical interfaces already configured on the pix or you specified a vlan when you setup the phy interfaces (which is still a logical interface even if it is the only one defined on the phy intf) then, yes you do need to configure the 6509 port as a trunk port. The pix will not send or process STP BPDU's, so you can still use the portfast or bpdu guard feature on the 6509 port.
You do not configure opposite vlans on the switch, what you do is create a mismatch on the native vlans between the 6509 and pix. Do not use a vlan that is one that has a non-pix active end-station, instead create a dummy vlan, do not place any ports in it and tell the 6509 that that is the native vlan on the pix port. On the pix the vlan assigned to the phy interface is considered the native vlan.
For example using the outside GE intf you would do this:
1. On the 6509 create the dummy vlan, say vlan 255.
2. On the 6509 modify the port that the ouside GE intf plugs into as a trunk port and set the native vlan to 255.
3. On the pix, the inside intf is already assigned to vlan 201, so all you need is to make sure that the pix default gateway is assigned properly (either the 6509 MSFC intf on vlan 201, or whatever router address is on vlan 201 (note the gw does not reside on vlan 255).
4. Do the same on for the inside GE pix intf. Maybe use VLAN 256 on the 6509 or some other dummy vlan other than the outside GE int native vlan (in this case, 255).
5. I assume that you have a MSFC or NFFC card in the 6509. If this is the case and vlans 201 and 216 are new vlans created for the pix, then you will need to insure that those vlans can be reached via the msfc. If you are pruning vlans to the msfc interface, then you need to exmaine the 6509 layer 2 config and add those to the allowed vlans to connect to the msfc interface.
Let me know if you need more help.
