Looks like HMOS was merely a marketing name for an evolution of the NMOS process:
The 7501 and its bigger brother, the 8501, were really just refined 6510s manufactured with Commodore's new HMOS (High-Speed NMOS, essentially NMOS using a new smaller process geometry) process. The 7501 was made using HMOS-1; the 8501 was made with HMOS-2 (a logical step to indicate the 6500s were made with the original NMOS process). Extra pins were added to the on-chip I/O port to accomodate the 264 series' more complex memory banking.
That's not directly addressing the question of whether it has no minimum clock speed: that's a feature of the circuit design, not the process. My suspicion is that it won't be a static design: there was no incentive for Commodore to make something like that, and they were famously cost-conscious.
Edit: Oops, I said
Even the 65CE02, which I think never sold in volume, was CMOS but still with a minimum clock speed.
and that's completely wrong! It has a minimum clock period, and therefore a max clock speed, but it does not have a minimum clock speed. As is normal for a CMOS design, it's a static design. This weakens my argument: the question is why did Commodore make this? Given they didn't sell it in volume, perhaps they didn't know either...