I'm guessing you're using setlimit incorrectly. I don't know how to use it though to tell you what "type" is.
As far as I know, URS limiting of items like dynamite was based on my old unolimited.
Within that, if you set the server var to 0, it would still allow <groups you specify> to go past <server limit> by <some number set in a cfg>.
Now, I've not looked at this code in a long time to know.
I've no idea if sbox_maxdynamite is still a valid server cvar.
But if you configure this addon correctly, and the sbox cvar still exists on the server, and this addon sitill works, I'm guessing it should allow some groups to set dynamite.
I'm sorry, but I don't know more than that.