Agassiz was closed off sometime in the mid to late 80's. So, it was once legal to climb. There is a climbers trail that leads to the summit. There really is no reason why this trail cannot be used. I have heard that there is more to it then the rare plant. And that it is one of the Navajo's Sacred Mountains. Due to respect for them only Humphry's is open.
Anyway, I've always thought that protecting a rare plant was a really dumb excuse. One trail is not going to make it go extinct.