Sorry, I edited my post as I was on my phone and kept copying and cutting somehow. Totally not adept at that so apologies if it was all jumbled!
But no, I don't think it's so much that they assume he's up and not bother. I think it's just that they consider him a non-factor at this point. Even Skye didn't nominate him this past fortnight and she has by far taken the brunt of his shit from what we've seen anyway. She goes from giving him 4 points, the max she can give, the week before the Sanctuary to just forgetting about him now. He'll obviously be up again but the HMs aren't thinking with the mind that the public are. They want him out as he "deserves it". They want him to stay because he's typically easy to live with and more importantly isn't going to win.
The week before Tully went home last year, she'd been given no points and both here and SM went into meltdown. Including me. Because I was sick of her crying and my friends had been shipping me cash from the US to vote for them to make it happen. Especially because she'd been up for eviction the previous week with a whopping 3 nomination points in a pool of six and her three points were only given by Matt who had the power plus could wipe out 2 of the HMs total votes so he saved himself and Ed and put her up. And she survived that week too and the Internet broke as it was the first chance to get her out after Tahlia spoke out. That's when I learned the HMs know... as annoying, aggressive, whiny, tomato-faced, cheating, etc a HM is... when they have no hope of winning, it's better to keep them around unless you think you're well and truly fucked with no public support and are up for eviction. That's the only time you'd want them in the line up.