Yes, still susceptible if the user enables accessibility permission for the malware app when prompted.
https://grapheneos.org/usage#accessibility
Third party accessibility services can be installed and activated. This includes the ones made by Google. Most of these will work but some may have a hard dependency on functionality from Google Play services for some of their functionality or to run at all. Accessibility services are very powerful and we strongly recommend against using third party implementations if you can get by well without them. We plan to add safeguards in this area while still keeping them working without problematic barriers.