Shannon Chan-Kent - Maryoku
Scott McNeil - Shika
Maryke Hendrikse - Ooka
And I was right that Chiara Zanni is in it, thus she must be Hadagi. I based a few of my guesses on watching clips of other things they've done, to pinpoint the voice actor if they hadn't done anything I recognized, which was kind of funny when I was watching Death Note clips of Misa, trying to see if the voice sounded closer to Maryoku or someone else.
Looking up the VAs, I noticed that a few of them were in the same titles over and over again, which means that most of them are in the Ocean Group dubbing company (they do a lot of Viz-related dubs). I also noticed that some of them were in the dub of Powerpuff Girls Z, which surprised me because as far as I'd heard, it hadn't come out over here yet. When it came out in Japan, I watched about the first twelve or so episodes and then just read Moetron for any more info I wanted, since their posts were usually more interesting than watching the series. And it was Moetron that gave me the info I wanted to know: apparently, the dubbed episodes haven't been shown in the states yet, but have aired in Australia and the Philippines. But the real reason I'm bringing this up is because they linked to some clips that have been put up on Youtube, including a clip with the Gangreen Gang, and when I was watching it, I very nearly said "Ace is Ikura!" outloud. And sure enough, it was Andrew Francis. Also, Mark Oliver (Grizzle's VA) is Him:
One more thing. While pinning down whether or not Maryke Hendrikse was a close enough match for Ooka, I watched a little bit of Barbie and the Diamond Castle, mostly the part where her character gives the backstory on the villain of the movie, Lydia, an evil ex-muse who trapped two others, and I saw something that just made no sense to me. You see, in the flashback we see the three of them before Lydia turned evil, but while the other two are wearing simple tunics, Lydia is already decked out in her villainwear. I mean, normally you'd think a muse that turned evil would have an Evil Costume Switch, not be Obviously Evil from the get-go (and to be fair, her flute does get an evil makeover), especially when the other two seem to have some kind of muse dress code going on. Unless this was a gradual thing...first, she traded in her flower headband for thorns to hold her bun, then she started playing death metal songs on her flute, and then came the outfit. All the clues were there, but the other muses refused to see the truth about what was happening to their friend until it was too late. Either that, or since it was Melody's flashback, she just remembers it happening that way ("All the muses were nice, except for Lydia, who was evil. Evil, I tells ya!").