I've found that you can change E-P1 files so that Aperture will import them. Make backups of your files first, obviously.
Get hold of Hex Fiend (I'm a sucker for a silly name)
http://ridiculousfish.com/hexfiend/
In Hex Fiend open the E-P1 .ORF file you want to import
Hit Apple-F or Find... from the edit menu
In the top box put E-P1 (make sure the ASCII box not the Hex box is checked)
In the bottom box put E-30 (again, make sure the ASCII box not the Hex box is checked)
Press Next then press Replace, there's only one string that needs changing.
Close the search box.
Hit Apple-S or Save... from the file menu.
Voila. You can now import that raw file into Aperture.
Obviously that's not very useful because you don't want to be going through that rigmarole with loads of images. But at least it means you can compare the Aperture Raw conversion with other options. <Edited by Host>