Older versions of the gpu pluggins can be used.. Very old mind you.. But they don't run as good as the impact renderers themselves.. The newest renderers are 1.11 version.. You can find them at
www.zophar.net in the psx pluggins section.. The newer pluggins like petes and lewpys don't work or don't work well with impact and is not supported so..... stick with the impact renderers..
To use the psx gpu pluggins you have to rename them to "renderer.ipc" then put it in the main impact folder.. I used to do this with old software gpu pluggins for psempro.. They worked, but not as good as the impact pluggins..