Hope I understand the question.
You can always create an iframe with the content of another page ( with the list of members) of another wiki!
BUT: if this wiki is private than only the (logged in) visitors with the rights to "read" the private wiki are allowed to see the embbeded content in your iframe.
a link to this would do the same - but unauthorized people wold land on the landing page defined in the site manage…
I try here an iframe of my private site - you can not see any content except the landing page:
A) In case you have the rights you can click on teh names and change their admin rights.
- but you can include on the "landing page" at least the module members command to show for foreign people who are to ask for membership…
B) in case you make this iframe on your private site with the content of the public - you can click on the site manager of the public and change their admin rights on public and later invite them on the private…
C) I have no idea if this works with unauthorized people - I have to test it later logged out..