Yes, it will work just fine. All models of the HW-19 use the same high-torque motors that mate well with a wide variety of platters. Since the TNT Superplatter is so much heavier, you'll for sure want to use the TNT's bearing assembly.
One thing to consider, however, is does your Superplatter accept the periphery ring clamp. If yes, it's a different diameter than the Mk 2/3 platter, and you'll need to get a different drive pulley from VPI to get the right platter speed (unless you use an SDS).
A word of advice, and if you have not already done so...to take your 'table to an even higher level of performance, upgrade to the stand alone motor assembly (SAMA). This upgrade takes the motor off the frame and eliminates any possible way for motor vibration to get into the plinth, bearing, or tonearm. Doing that upgrade will essentially take your 'table to a Mk IV-Improved level.
RE: the rubber washer, yes, you want to use one. Size is 1/8" (3.2mm) thick; 7mm ID; 1.25" OD. You can get them from VPI. I highly recommend the Grungebuster washer from Herbie's Audio Lab. Check near the bottom of the page here: http://herbiesaudiolab.net/washers.htm
Good luck with the upgrade.