It looks like it's possibe to allow non-admins to use the grappling hook by taking out the line:"denyCmd = hook" under "Defaultefault" in the DF_admins.txt file.
Suggestion: Make grapple work only when it can attach to a visible surface. Right now one can grapple to anywhere, even the sky.
Also would be great if there was a cvar for setting a rope length limit.