Hi, Ilkka.
At this time, the required capability to check in attendees is edit_posts and that might also work for accessing the attendees list. You’ll need to do some trial and error to make sure it works exactly as you want.
https://wordpress.org/plugins/user-switching/ (third-party, not guaranteed or supported by us) might be helpful to you.
I believe you’re requesting the same thing as one of our existing feature requests: https://tribe.uservoice.com/forums/195723-feature-ideas/suggestions/5575496-specific-roles-capabilities-for-event-ticket-check
Please do add your vote there.
This allows us to gauge interest in this particular feature request, which helps us prioritize our development efforts.
Thank you.