Even though a drumhit isn't a particularly 'musical' sound, it still has a tone and resonates at a certain frequency. And frequency = pitch. From my understanding (correct me if I'm wrong any drummers out there!) the drums in a kit should all be in tune with each other, and preferably should sound in tune with the rest of the instruments too.
What 'in tune' is comes down to your personal taste, because you're building your own kit, but you can use features in UB and the EXS to experiment with the pitch of your drum samples.
A good example of drums that need to be in tune with each other is toms, because they a have a similar purpose in the kit, but have totally different tones. I found this on a drum tuning website:
"You must try to get the toms to sound like they belong in the same kit. For best results on a standard 12", 13" and 16" tom set, pitch intervals between drums should be a 3rd or 4th apart (as a general rule). It is usually best to start with your lowest tom and work up from there. Also, try to get tone quality (resonance, decay) as similar as possible."
So when you build your kit in UB or the EXS, first make sure that your samples sound 'in tune' with eachother, like they are all part of the same kit. Then see how that fits with the rest of the track. You can fine tune the pitch of the samples in UB by moving the pitch slider on the oscillator with the sample (I think its OSC 3). (Don't worry about what pitch the slider actually says, because it always defaults to 'C'and your drum samples won't be 'C'.) Just move it around until you find the best sound for your track.
If you have to make extreme pitch changes to get the drums in tune, you should try a different drum sample to begin with, because changing the pitch is also changing the way the sample plays back.
I think the pitch function in the EXS lets you make more precise pitch changes, you can check that out once you get onto that tutorial.
If you're having trouble hearing the tone of a drum hit, a good method is to listen to the sample backwards - that way the sharp attack of the drumhit won't obscure the tone.
Hope that helps!
And hey Rounik! how are you? I'm good, just working on one track actually, not an album. It's a remix of a friends tune - its going to be released at the same time as his new album, which has been delayed... So I guess that gives me more time to put my money where my mouth is, and make sure my drums are in tune!