Although this is an old question i'm going to answer anyway, because i had the same one recently.
Yes, we have Richfaces working behind an Webseal (v6.1).
With an Webseal there are some considerations concerning Ajax. You can find some hints in the following manual:
Basicly you have to configure the junction correctly:
-activate scripting support
-extend the list of scanned content types
Nevertheless, we still had the same problem as described here.
We solved it by using an transparent Junction on the Webseal so the need no rewriting any more. Transparent junctions are only available since Webseal 6.1.