You could/should have asked this in the existing EZD/SD thread (just for continuity and consolidation of all info)....but no big deal.
SD has several humanize options. For most of the kits/drums in various sample packs, these are all almost always on, and should be left on. SD is already doing most of that humanize stuff for you.
Now....should you do additional timing/velocity randomization withing the MIDI drum editor...?...it's up to you.
I'll do more global velocity adjustments in the drum editor...like say, limiting the velocities between min/max values, but only when I'm dropping hits in from scratch. I find that if I grab an existing MIDI groove (EZ/SD packs come with man grooves)....there's not as much need to do that, as the grooves were played (not programmed), so there's already plenty of "human" feel there....both for timing and velocity. You can see it in the drum editor that nothing is rigidly quantized when you drop a decent groove in there.
That's not to say that I don't also make additional edits in the drum editor....I'm just saying it's all about how it sounds to you. There's no magic single setting that will work on every kit, every groove, every song, but you can probably to OK just letting the SD humanize options do their work....and then maybe to some adjustments of your own in the MIDI drum editor. Lightly nudge timing/velocities to suite your taste...but really, you have to LISTEN to how it sounds, and not just move stuff around to make it more random by the numbers.
IOW....there can be a big difference if the hits are randomly ahead of the beat or randomly behind it....depending on the groove feel you are after.
One thing, most of the sample pack grooves are short...so when you use them and copy/paste/copy/paste to extend them for a few measures...you then should make some effort to change them a little, in addition to what SD is doing with the humanize options, otherwsie a 2 measure groove X 10...is going to stick out if it's not randomized a bit. We're talking about giving them some minor differences....nothing crazy/extreme.
Also....ain't nothing wrong with having a decent amount of hits be ON the beat. That's where most of them are supposed to be if the drummer is steady.