No this is not possible for several reasons...
- first, this has nothing to do with anope.. showing joins/parts or the user list is all done by the ircd anope has no control over anything that happens between the ircd and the server
- secondly, even for doing this ircd side, it is technically impossible to show the user list, but hide joins and parts on the ircd side.. if the ircd does not send join and part information to the client the client will not be able to update the user list of the channel.. so you cannot have clients show a user list without sending them updates for that list in the form of joins or parts.
It is an all or nothing thing.
the option of hiding certain things like joins and parts can only be set in the clients, not on the server side...