No, underhand bent over rows are not dangerous for the biceps any more than a mixed grip dead lift is.
Dude, both of those lifts are far more dangerous than the overhand version.
...a mixed deadlift grip IS dangerous for the bicep tendon, most people who tear biceps while deadlifting tear the bicep of the arm with the underhand grip.
...underhand grip bent over rows ARE dangerous, most people who tear biceps (lats seldom tear during rows) while doing rows tear the muscle while using an underhand grip.
How do you guys not know this stuff?
The Luke