Hegemony runs great under Parallels!
Minimum specs for Parallels and Hegemony:
Recommended you have a video card with at least 512MBs of memory with 256MBs available to Windows. This will let you play at most common resolutions (you won't be able to do 1080p equivalent resolutions, but you will be able to do most smaller monitors). You can get away with a video card with only 256MBs of video memory sending 192MBs to Windows, but you will need to reduce Hegemony's graphics settings to near minimum and not play over 1024x768. Hegemony works well with non-standard resolutions, so you can fit it to however big your Parallels windowized display is if you have enough memory. However, Parallels itself is maxed at 256MBs (Hegemony's recommended minimum) so you won't be able to drive any really high resolution displays at full screen, even if your video card has more memory available.
The other specs (1GB or 2GB memory, 1GB hard disk space, etc.) from the Windows minimum requirements mean that you need to have at least that much available for Parallels. Ergo, if you have a base level iMac, you probably need to add extra RAM to it in order to have enough RAM available that the Mac side does not lag up while sending 2GBs to Windows.
I've have great success running and testing Hegemony over the past 8 months on Parallels with no evident issues caused from the translation from Mac to Windows using Parallels.
I can confirm that these settings work with both OSX 10.5 (Leopard) and OSX 10.6 (Snow Leopard). Note that you generally want to leave at least 128MBs video memory available for the Mac side to avoid lag (especially important in Leopard, less so in Snow Leopard). Hegemony does not make much use of multithreaded operations, so you have no need to assign more than one CPU to Parallels.
Mac Pro (2x 2.8GHz quad core Xeons)
geForce 8800GT primary video card + low end ATI secondary
Plenty of spare RAM
Plenty of spare HDD space
All tests were done under Windows XP
If anyone has tested the game on iMacs, Macbooks, or Mac Minis, post them here. I know most of the older Mac systems will have trouble allocating enough video memory to drive Hegemony, so I suspect many will not work without Boot Camp.