Doesn't need to happen often, its a possibility for x number of people passing thru the borders any given day. They have the legal right to force your biometrics to unlock your device. Removing it ahead of time is prudent.
If you breeze thru no problems; no harm no foul, just add your thumb again.
There's nothing stopping creators from doing sponsored videos and/or sharing their liberapay/opencollective/patreon on peertube, they even provide a dedicated place for it.
Most of the youtubers I follow claim YouTube's direct compensation makes up very little of their overall income, especially since YouTube keeps lowering the compensation/demonetizing everything. Most of their income comes from sponsored videos, patreons, and merch sales. Maybe it depends on the youtuber but it seems consistent with those I follow.