I've used their Rac and Rho antibodies, but for human samples. I think the antigen used for these antibodies is of human origin, and I wouldn't expect it to work in yeast cells. If you can't do traditional pull-down assays with the PBD domain to detect the active conformation of cdc42, there are some immunostaining and FRET-based assays that might be feasible for yeast.

Here you have a searcher:

http://1degreebio.org/