In fact, I seem to recall a similar discussion during the first bake-off, where we had a sonnet (I'm blanking on which one) that dealt with whips and torture, and there was some discussion about the need in that context to bury the emotive, strong words within the lines since giving them the extra prominence of rhyme might be overkill. Anyway, I don't remember the details, but interested parties can dig up the old bake-off and have a look.
I'd also note that many lesser sonnets are bad because they save all their good words for the rhyming position, and the interiors of the lines seem like nondescript and boring ways of connecting the rhyme words. I'd say that rhyming on "unimportant" words, just to keep the sonic environment in place for the rest of the words in the middle of the lines, is perfectly justifiable. If a word isn't suitable for the rhyme position, perhaps it's not doing enough in the poem, period, and shouldn't be considered for the middle of a line either. Whether a word can be used to rhyme should depend, I think, not on its importance but on the same considerations that govern the use of enjambment for any part of speech, e.g., rhythm and syntax.
I was recently told that Rilke was the first poet in German to rhyme words like "und" (and), which raised many eyebrows at the time but is now considered to be acceptable.
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