Just want to share my experience in this matter...
I recently bought a Gameboy player (last month) and finally got it a couple of days ago. I knew the seller wasn't offering a booting disc but it was so cheap I thought I had nothing to lose, after all I had read somewhere in the forum that it was compatible via swiss.
However, when I tried a shrunken NTSC iso (about 2 MB) with swiss it didn't really work, a black screen showed up and nothing happened after that. I decided to try a PAL version (1.46 GB), this time I got a warning: "an error has ocurred" (High Patch ON). Then tried resetting the console and booting the PAL image one more time to notice how the dvd drive was making a clicking noise two or three times before showing the warning, like if it were looking for a DVD.
Since all my GB games are made in USA I thought it would be a good idea to find an untouched NTSC iso for the Booting disc, considering the possibility the NTSC iso I had was faulty. I was able to find one eventually, it booted OK with swiss but behaved exactly as the PAL one: Clicking sound, then the error sign, then nothing else.
Finally decided to burn the image into a mini DVD (ritek04) at 2x to see what would happen... finished burning, loaded it up and BAM, Gameboy Player screen shows up. Tried Pokemon Crystal and worked but the best part is that it works with the EZ-FLASH IV!
So, while we wait for these guys to check how to get it running via swiss, know it can be done with a miniDVD.