Is A DSLR APS-C Camera More Likely To Create Creamier Bokeh than A Mirrorless APS-C?

There are not many fast lenses in native mounts for mirror-less cameras, and also not many fast tele photo lenses. That is the only reason why you might find more examples of "creamy bokeh" with DSLR's.

But you can use adapters and mount almost any lens on mirror-less camera. There are tons of option for manual focus solution, which for your intended purpose should be fine.

With NEX you have also possibility to use either LA-EA2 and Sony A-mount lenses which will give you Phase Detection AF, LA-EA1 using contrast detection AF with some lenses, or Metabones Smart EF/NEX adapter (and some cheaper knockoffs), that in its last version allow Contrast Detection AF with some Canon EF lenses, including Canon EF Macro 100 f2.8 L IS. (But the AF is very slow).

Mounting big lens and adapter however, usually means much larger setup than a native mount one, so you wouldn't gain much in comparison to the entry level DSLR in terms of size.

Regarding bokeh, there are many things that enters the game, but nothing to do with a mirror-less or DSLR.

From those many things that can influence the bokeh, focal length, aperture, distance from the subject, distance between the subject and the background, lighting, shape of the aperture blades, structure of the background, colors, etc. are the ones to first learn about.

Here are few shots with NEX 7, that shows kind of "creamy bokeh" with flowers...

Hope it helps.

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