Huh, then I guess both the site from which I found that chart and I were a little inaccurate.
Doing a little more snooping around I discovered that several H97 chipset owners (and some H81, B75, H87) were able to overclock their processors (not just Devil's Canyon or g3258,) but only on select manufacturers' boards and only after a BIOS update. However, their maximum, stable clock speeds weren't nearly as high as Z97 chipset boards.
...so sure, H97 can overclock, but it depends on the manufacturer and the BIOS update.