Hmm. Are those terms interchangable? The only way I'm familiar with the term "bootlegger" is not the way you seem to be asking. And if by masher, you mean those people who take elements of a different songs and combine them into a new song, then I would say yes, there is an art to that, even if I feel the novelty of it wore off awhile ago.
If I'm missing the point, please let me know.
No, you got the gist of it. The way I've seen it is bootlegger is someone who uses a ton of unlicensed samples, but arranges them around an original song, a masher combines elements of different songs, and a mixer only uses elements from one song, but arranges them in a decidely unique way, moreso than your average remix.