Although Zirin raises some interesting points, I would be pretty surprised to see any big leaguers sit out May 1 for political reasons.
I would also bring up an objection to this point Zirin makes:
The new reality was laid bare at this spring's World Baseball Classic: The U.S. team couldn't compete with its Latin American rivals, failing to even make it out of pool play.
In the WBC, the USA lost to Canada, Korea, and Mexico, so that team demonstrated that it could lose to pretty much any ethnicity.
It would be interesting to see if attendance is affected at any game however. The only team owned by a Latino, Arte Moreno's Angels are at home on May 1. Barry Zito is scheduled to start for Oakland against Hector Carrasco of the Angels.
There is one scheduled pitching matchup of Latino pitchers on May 1. That will be in New York, where Washington's Ramon Ortiz will be facing the Mets' Victor Zambrano.
The last time I can remember any players refusing to play over a political matter was back on April 25, 2000. That day, Cuban-American leaders in the Miami area called for a boycott that day to protest the Federal Government's handling of the Elian Gonzalez case. The Marlins drew 9,072 fans for their game that night, although they didn't draw well much of that season to begin with.
As for me, I might be spending my May Day here. I'm the guy on the right in the army uniform.