Will there be visible marks or scars in the donor area when completely shaved?

Any cut on your skin will leave a scar.  FUE will definitely leave a visible scar if you shave your head.

I assume you had an FUE and probably not more than 500 or so grafts.If these were widely distributed throughout the donor area it should be difficult to detect with the head shaved.Keep in mind though that each graft harvest site can leave a tiny white circular scar.

If you completely shave, I would do FUE over FUT (strip).  Reason being its much less obvious than a linear scar.  I also find that robotic FUE leave less of a scaring risk over manual FUE because of the delicate blunt dissection. Also, if you're really concerned, you can try scalp micro-pigmentation to the donor area to mask the FUE marks.  You can similarly try this with a linear FUT scar however it is much less noticeable again with FUE.  Good luck. Dr. Rome