I gather this is generally possible, as long as bulbs draw less power than the ballast can provide
Nope, you're thinking in voltage. With fluorescent tubes, you must think in current.
Anything you plug into mains power must be a constant-voltage device. Heaters are, and incandescent bulbs are close enough. That's where you get the misconception.
Fluorescent tubes are a member of the "arc discharge light" family. Once the arc strikes, they are nearly a dead short. The word for that is "non-linear". They need an additional part, a ballast, to limit current through them to avert their destruction. The ballast outputs the correct amount of current for the tube it is designed for... At whichever voltage that turns out to be.
However the ballast has practical limits to its voltage range. That limits which tubes it can work with. It may also have dual circuits to drive two tubes independently (and can work with one), or not. The upshot is the ballast has a data sheet (that link wasn't the data sheet) listing every combination of tube sizes it can drive. You need to go find that data sheet and look.
Now that we're thinking in current, the obvious answer is "probably not", the HO ballast would push more current than the NO tube is designed for.