Brush has auto-mask mode (a checkbox). It works OK I guess sometimes (other times not so much..).
Hoping for auto-masking improvement in Lr6.
YYes, I know that but this does not answer my question.
The answer to your question is:
No. (masking based on specified tonal range(s) is not supported).
And, yes - auto-masking brush is tone-sensitive and will mask, to some extent, based on tone (also color, I think, and who knows what else.. - it doesn't work very well in my opinion).
If this does not sufficiently answer your question, then perhaps you need to elaborate and clarify the question.