[_Microft]

The tickets aren't personalized (some regular monthly passes for public transport are/were though), so you should be fine. Since they aren't personalized and there is no way to check who the owner actually is, I would even expect them to be transferable.

Edit: looks like I was wrong -> see replies. You can also search for "9-Euro-Ticket übertragbar" (übertragbar = transferable) yourself to get a number of different German sources for that.

[dmurray]

Normally DB day tickets, even bought at the ticket machine, are not transferable. You have to write your name on the back - in theory, before the first time you encounter a ticket controller - and be prepared to produce ID matching the name.

[_ph_]

Honestly, this is the first time I ever hear of this, and I almost go back to steam engine trains :p

[germanier]

This ticket is personalized.