I suppose you could create a scheduled job where you: Get the users -> create user object -> include the user profile page in the user object -> index user objects.
If you are using UnifiedSearch, there are various ways to include the user objects in the unified search. Check out the documentation: http://world.episerver.com/documentation/Items/Developers-Guide/EPiServer-Find/11/DotNET-Client-API/Searching/Unified-search/
You can index any type of object with find so no problem at all.
We have approx 6000 users (in a separate db) and a dynamic user profile page that shows user details.
A user id in the querystring of the profile page is used to show a specific user´s profile.
How can we use Find to index this dynamic page for each user so that all user profile pages will be searchable?