Unfortunately it is not possible to play a VSTi (not a RR-sampler!) with RoundRobin MIDI alteration by hitting only one e-drum. We figured out in the German forum that there is only ArpacheSX working wth percussive sounds.
If you want to play a melody with pad-sounds you come to know that NoteOff events are needed at the same time the next note is played…
OK, the ingenious Bidule MIDI geeks are getting this one right! 
https://www.plogue.com/phpBB3/viewtopic.php?f=4&t=7773&p=41631#top
(3rd post, solution by user reezekeys)
But you’ll still need virtual MIDI ports to get MIDI from Cubase into the Bidule program and back again… 
Are you Cubase developers getting this one also right, only within Cubase (with a Cubase MIDI plugin)? 
Look what Bidule can do with it:
Melody-Play for e-drummers!
For example: Three E-drum pads; two for different melodies, one for stopping all notes…
http://www.plogue.com/phpBB3/viewtopic.php?f=8&t=7777&p=41657#p41657
The admittedly strong Cubase midi features meet their match 
(To give (non-)drummers an idea for drummer’s melody play : check the melody-presets with a Roland flaggship e-drum module:
