More importantly, the maps of this merger differ considerably, for example with regard to how far it's moved back eastward across the northern tier of the US: Labov et al. have it still out on the Great Plains on at least one map in the Atlas I think (hey, I'm on the road and can't check), while another of theirs shows it sporadic in Minnesota, most other maps put it in Minnesota, while Erica Benson and others are finding it in western Wisconsin today, where it's pretty salient to speakers.
I remembered this area, northeastern Kansas, as a place that should have the merger. So naturally I've been asking students and others what the chant is and I'm getting a real mix, some obviously merged, some in that unnerving gray zone of near-merger, and others clearly distinct, even among people who say they're from this general area (which I haven't defined, working on the fly). The Labov et al. map linked above does indeed show this as clearly within merged territory, while the old Wolfram map (the one with the merged area in crosshatch — it's around on the internet, I think) shows it near the isogloss, where you'd expect variation.
People truly do not seem very attuned to this: When I say 'oh, you say all those vowels the same/not the same?', I haven't gotten any responses like 'what, you think I sound like I'm from out west?' or 'yeah, that's how we talk; man, those Iowa people sound weird, don't they?' A merged speaker who turned out to be from South Dakota seemed to think her merger was somehow distinct (forgive the pun) from local speech. Matthew Gordon has done nice work in this general part of the country (with a recent story floating around many newspapers, see here) and he comments specifically on the low-back merger here, crucially:
Many language changes attract negative attention particularly when they are associated with young people. It is not uncommon, for example, to hear criticisms of the use of ‘like’ as a discourse marker, a feature common among younger speakers (e.g., “He like just came out of like the store.”). The cot/caught merger, however, seems not to attract any such stigmatization. In fact, people are largely unaware of it.That's how it sure seems to be in Kansas … even when the "internationally famous" school chant exemplifies the pattern.