Does major and minor simply indicate that the the third scale degree is either a major or minor third interval away from the tonic?
That might be a problematic way of defining it. After all, in "minor pentatonic," the third scale degree is a fourth above the first scale degree! But part of the point of modes is simply which note is the tonic. After all, all eight church modes use the same pitches. The difference is about which note is treated as "home base." So in C "major" pentatonic, the C is the note around which the material gravitates, while in "minor" pentatonic (or, as the Kodaly system calls it, "la-based" pentatonic), it's A. One could imagine modally ambiguous musical material that could make it hard to decide which one it is.
But people do in fact try to call some of these modes "major-ish" and "minor-ish," as in this table. And yes, this impulse is closer to what you described: "minor pentatonic" does in fact have a note that is a minor third above the tonic, even if it's not the third note in the scale. In my opinion, this isn't particularly helpful or even appropriate; these modes aren't major or minor, just similar in some ways. I don't see the value of grouping them, and that wasn't a way of thinking when they were created.
Now this gets confusing, but your question is a different matter. For this conversation, let's treat the word "scale" as meaning "a set of pitches." (It's not just that, but let's use that definition for now.) Meanwhile "mode" can talk about which of those pitches is the tonic. So the garden-variety major and minor are both "modes of the same scale" (all the church modes are, and these are just Ionian and Aeolian). And "major and minor pentatonic" are both modes of the same scale.
So, in theory, any scale can have modes, just by "centering" one note or another from its set. In practice, this often doesn't make sense. For example, the whole tone scale would sound the same no matter which note is the tonic (that's kind of its schtick), and the octatonic scale is similar. And many scales are closely tied to specific practices, like the "gypsy scale" and blues scales; creating modal "mutations" of them would be a fanciful departure from a very practical structure. So while you could derive all kinds of modes from all kinds of scales, it's not always an idea that makes sense, and it doesn't always make sense to apply the words "major" and "minor" to them.
That said, there are a few more where the labels are used. There's a "major" and "minor" blues scale, and there's mention of a "gypsy major".