I have never seen the impedance curve for an H2 published.
On the other hand there is a plot of impedance of what I believe is a regular old Heresy in the collection of papers called, The Dope From Hope.
You should search the technical section for the word dopefromhope
The specific paper is near the end.
You will see that the paper reports that the high impedance reduces distortion when an amp is driven to near clipping. Whether this applies to SETs I don't know. (Given the low power, it seems to me they are always being driven to near clipping. Smile.)
If I was concerned about impedance magnitude and compensation:
I note that you can put an 8 ohm resistor across the speaker with impedances of 10 to 70 ohms. You wind up with parallel impedance ranging from about 4.4 ohm minimum to about 7.2 ohm max (you can and should do the math to check). I seems to me that the 4 ohm tap on the transformer could drive this load, which probably has less variation than other speakers.
Of course a 10 ohm or 16 ohm could be used too with somewhat similar results.