When studying non-chord tones all the definitions use steps in the diatonic sense, but what about non-chord tones in pentatonic melodies? Are melodies written in pentatonic scales considered "steps"? Or are some of them still leaps?
Steps are the intervals between two notes of, generally considered, diatonic scales. Thus they're either major 2nds or minor 2nds. Also referred to as conjunct motion, semitones being half steps, tones being whole steps. For example, in key C, D>E is a whole step, while E>F is a half step.
Any wider intervals than those are skips or leaps, also referred to as disjunct motion. Such as in the C pentatonic scale between E and G (m3). So, in the pentatonic scales (both major and minor) there are steps and skips.
Whatever scale is in consideration, those will be the intervals, so it doesn't really matter which scales are in discussion. All full major scales will only contain steps, while pents (and others, like harmonic minor) will contain both steps and skips. The fact that notes are non chord tones isn't a consideration. In a melody with consecutive notes of a semitone or a tone maximum, those are steps; anything larger are skips.
It all depends. The concept of a step is usually tied to a very specific concept of harmony, so if you want to use to for other situation you need to generalize it. But if you define a step to be the interval between to adjacent scale notes you get a sort of inconsistency in your terminology and common terminology. In a pentatonic scale we expect to have two steps and then a jump.
More general a scale can be taken as subscale of another scale. Should the terminology then be consistent among these scales?
It's defined by context. If one is talking about the scale itself, then one tends to refer (colloquially) to the "steps" in the scale. However, if talking about the intervallic content, then one is likely to describe the larger-than-a-whole-step intervals as "skips".
The ideas of chord- and non-chord tones is one that doesn't really apply to pentatonic scales, at least not in the same way it does to diatonic scales. Neither the "building chords in thirds" nor the "every other scale tone" applies cleanly to pentatonic scales, so one can essentially adapt the concepts as is convenient to the scenario at hand.
In the pentatonic case, it's probably most convenient to think of notes in the scale and notes not in the scale, and make this synonymous with chord tones and non-chord tones. That will give a consistent definition regardless how one chooses to define/build chords within the scale.
For the purpose of ornamentation, then, it becomes a question of whether the ornaments stay within the scale (in which case some might involve the "skip"), or whether ornamentation can use notes outside the scale.