This has compatibility for the hhkb layout for mx boards, but this will not work for the HHKB keyboard (topre), unless your hhkb has topre to mx sliders.
Honestly, I have mixed Cherry and DCS keycaps without too much issue.
They are very close in profile, as opposed to other profiles such as DSA or SA.
I have used DCS together with ePBT 9009, for example. Your fingers won't slip up too much. You could probably use the Sleeper accent keys on a Cherry-profile board without too much issue. SP should really produce more such sets if that is the case.