A very legitimate question, David, especially after reviewing this Fed caseplay:
8.1.2 SITUATION: With R1 on first, B2 hits on the ground between first and second. R1 is hit by the batted ball, or he hinders F4 in his throw to first.
Ruling: R1 is out and ball becomes dead when the interference occurs. If the interference clearly prevented B2 from being put out at first, he also is out.
While the umpire certainly has the right to call out B1 in your scenario, I think most would base their judgment on whether a DP was a possible outcome of the ground ball had the play been absent of the interference. While that may not be exactly per the rule, I believe that is how most that I have seen apply their judgment.
Just my opinion,
Freix