HUGE FLIER, it is not my friend. At least not on the basis you state.
he probably NEVER played in a German League. He played (and most likely learned) at a U.S. Div I school, NC St. (Patriots.com excerpt below).
Yes, same like Vollmer he may be behind guys his same age in technique and knowledge, but if he has genetic talent and willingness to work/learn; he could have the potential to stick. And 4 years of NFL footage while he was on a team that holds JOINT PRACTICES FOR A WEEK each year with the Pats, i would think means BB and the scouts decided on more than the basis of "grainy footage".
I have no clue about his talent level, but i can take those 3 FACTs (nc St, nyg, 4-yr pro) and say your scepticism is all wet.