Recognizing Romero as a saint won't go over too well with those who see him as a communist and as a person who was leading the country down the path of revolution. The Nicaraguan Church's support for the removal of Somoza was important to convincing many Catholics to give the broad-based but Sandinista-led insurgency an opportunity. Romero wasn't at the point of throwing the Catholic Church's support behind the guerrillas (he had just supported the October 15 coup) but there was fear that he would eventually. That was unacceptable.
To the extent that I thought about it at all*, I had typically thought of canonization as a dependent rather than independent variable. In other words, politics is involved in determining whether a given person gets chosen, but being chosen doesn't create any new political effects.
I don't find Padgett's argument compelling at all--will gang members stop fighting because Romero is a saint? There are tons of saints and that hasn't stopped anyone from doing all sorts of horrible things. Following Mike's point, I think it would be interesting to research the political effects of canonization. I would hypothesize that the most likely outcome would be dialogue--it makes people talk about the person and his/her political context. But maybe that also can have a negative effect on deeply divided countries by making one side dig in more.
*not being Catholic, I find the entire process both fascinating and a bit bizarre.