Hello,
Now it is possible to share a collection which a user who is not granted to access Alteryx server.
We use AD to grant users access to Alteryx Gallery. However, when a user is not in this group, it is still possible to choose him as a person to share.
In my opinion, such user should be indicated as someone who won't be able to use a shared collection, or he should be presented at all.
Best,
Piotr