Thank you so much for taking a moment to get in touch, your time is greatly valued.
Although it is possible to moderate markers which are submitted (meaning a marker need to be approved before showing up publicly), it is not possible to show a marker (or a set of markers) to only a specific set of users.
We may consider this in future, however it is not currently in our development schedule.
I hope this helps? My apologies for any inconvenience caused.