As far as I know of, there aren't any issues with an uneven number of WCCP targets. (wccp on the ASA is mostly standard...)
Just make sure you've got the ACL setup correctly so the connections don't go through multiple WSA's...
I have a problem With WCCP and Ironport S160/S170 running 7.7.0-725. The WCCP only sends traffic to one of the Ironports at a time.
There's an Access-list that includes the two Ironports;
SW-D12-01#sh ip access-lists
Standard IP access list WCCP-Group
13 permit 10.50.0.211
12 permit 10.50.0.212
For some reason the WCCP only send traffic to 10.50.0.211. If I remove the .211 from the config it sends to .212..
On the WSAs, go to Network > Transparent Redirection
Open the service you defined.
In the top box pick a load balance method... I use based on Client address...
Click on advanced, pick Allow Hash or Mask (that way the WSA's negotiate)
I don't remember where I got the mask value from but I set a Custom mask, and used 0x526 (binary is 10100100110)