Just FYI, the method by which Omeka detects ImageMagick results in an apparently incorrect "fails" message in the settings panel under Path to Convert, at least on MidPhase hosting. After speaking with support at MidPhase, they inform me that the path to ImageMagick is usr/bin and this does seem to work, despite the "fails" message. They said this could be due to the fact that they have "compiled the binaries" for Image Magick in such a way that there is "not actually a path."
Not sure what all this means exactly, but thought it was worth mentioning in case it can be addressed in a future release. And also of course in case someone else is stumped by this apparently incorrect error message, I suggest just trying usr/bin to see if it works anyway.
One last note, there is also the possibility that this particular issue is related to my server migration process.
Cheers - E