I think you can wear them. Otherwise my teacher wouldn't have suggested it.
I just can't take it when people nearby are chatting--I can tune out anything that's lower than that, but when it gets to bands doing sound checks right below you, the score's going to drop a bit. Come April or so I'll start taking tests in the library and see if I can get used to a low level of noise, but I'm wearing the earplugs anyway so I don't get distracted.
Ah, my dad said that earplugs are verboten because of the possibility of them being audio transmitters in disguise. I guess I wouldn't need them on the day of the test, though--given my test site, it's pretty secluded and quiet enough so that I would be able to take it and not want to kill the nearest noisemaking thing.