No, it is not. Try and you'll see. Access has built-in checks that
prevent it from replicating a workgroup file.

A workgroup file, like a front end, is not something that needs
two-way updates, unless you are allowing your users to change their
own passwords. Also, a workgroup file is fairly static -- after it's
in place, you don't generally need to change it, except to add new
users. That can be done by simply replacing the old workgroup file
with a new one.

I'm not sure I can think of a solution to this that would make it
possible for the users to change their passwords and have them
retained when you send out a new workgroup file.

For me, I only do replication for single-user installations on
laptops and a home base with multiple users. The single-user never
really needs an update to the workgroup file once it's initialized,
so I don't see an issue there.

It's only if you're using replication to connect two or more
multi-user sites, and I just don't do that any more -- I would
always use Terminal Server, in which case you'd have a single
workgroup file for everyone at all locations (since everyone's
working on a single Terminal Server).

I'm not sure why you would need to replicate a mdw file.  Care to expand?