I don't own those games so I can't test them.
Even if you are right the whole point of this was if a SD Card or a USB Device was a better choice.
In this case an SD Card would be the better choice. We don't know when or even if DM will be released. But right now we do have DML.
And if you are buying a USB Drive you are much better off buying a bigger size one than 32gb such as 500 or so.
Okay... how do I put it bluntly for you...
Let's assume that the speed is the same (it's not, but for the sake of the argument) and that the compatibility, as mentioned by the creator, is the same aswell.
Wii takes SDHC cards, which are restricted to 32 gigs max. HDD's don't have that restriction, assuming that you'll be using FAT32, the only restriction you have is the 4 gigs per file, which is not a problem as all Gamecube games are under that size due to the medium used. So.
A clean Gamecube image is about 1,6 gigs big. Let's use clean ones in our calculations.
32/1,6 = 20
HDD = Whatever size you want = However many games you want.
HDD wins. Flawless Victory.
So yes, if you don't like swapping mediums, which is the very idea behind loading games from mediums other than discs, the HDD is the natural choice due to capacity alone.