I have flown every variety of DC-9 except the -20. Rotate at approximately 3 degrees per second. Two engine pitch for climbout will be around 13-18 degrees nose high depending on a host of conditions such as weight, temp, altitude, engines installed, etc. Too many specifics to generalize, but 15 degrees nose high is the normal two engine attitude plus or minus a couple of degrees, with single engine climbout attitude being maybe 4 degrees lower initially (12.5 is a common initial target). It is rather difficult but not impossible to get a tailstrike on takeoff in a DC-9, much harder than a 757 or 767-300 for instance.
I don't have my manual set handy (I am not currently flying the DC-9), but I recall that a tailstrike happens on takeoff at a tad more than 11 degrees pitch, which seems to square with what Tb727 is saying. If you rotate at the correct speed at 3 degrees per second you won't hit the tail.
There is absolutely nothing novel or unpredictable in the handling of the DC-9; rotation is entirely conventional.