There's not really an easy solution to this. One of the two packages needs to be in a namespace, so you can differentiate between the overlapping names.
I've advocated putting all of NGUI in a NGUI namespace earlier, but it's a bunch of work and it would break backward compatibility entirely, so it hasn't happened.
Alternatively, you have to refactor the name of one of the tools - I don't recommend NGUI's, since so many other files use the type.