WAAS versions greater than 5.0 all handle Citrix ICA with no configuration necessary, it is simply plug and play.
WAAS does not turn off compression, it removes the Citrix compression and uses its own compression that is better on your WAN, then puts the Citrix compression back on at the other end. The client sees the packet exactly as it was sent from the Citrix server, with Citrix compression. WAAS is transparent to your users. My WAAS system is currently claiming a 27% reduction in bandwidth for Citrix. Other acceleration is much more impressive, like file copying (CIFS), web traffic, replication traffic, and SQL, all of which consistently show 70%-95% reduction in bandwidth. All of which are also plug and play with WAAS.