I think that’s the catch in this kind of takeover coup by mass amnesty. Mexican immigrants are not that politically motivated and I don’t think more than 20% of them would actually try to register and vote, because of concern that they would identify themselves as illegal immigrants and then they might be deported later if the mass amnesty was overturned (by courts or congress).
So the number of votes lost by the democrats among legal citizens in 2010 would be far more than the votes gained by illegals voting. So a mass amnesty by executive order would very likely backfire disastrously on Obama and lead to a huge number of GOP victories in November. So I think the rumors are probably exaggerated and this kind of stunt isn’t going to happen. Not that this administration wouldn’t want to do this if it would work, but their problem is that it would backfire badly in the first election and lead to GOP control of both the House and the Senate.