The md5 checksum is actually mentioned here on the RHDN project page
But in case you cannot acquire that particular overdump, you can convert the regular 3 megabyte NoIntro rom quite easily. You just need to duplicate the last meg of data (0x200000-0x2FFFFF unheadered) and append it to the end of the file. This can be done with a hexeditor for example. Not ideal, but I've checked and the resulting file has the exact same checksum.
As for whether it's fully playable when applied to the normal rom, it seems that a few bytes in the 0x3df600-0x3dfc7f range are different than they should be (0x00 instead of 0xFF). All of them seem to be graphics (I see CRITICAL and some numbers there). Nothing totally game-breaking.
The lack of the Aeon Genesis splash screen isn't symptomatic of a badly patched ROM. The patched overdump doesn't have it either. It was an oversight, by Gideon's own admission.
EDIT: For what it's worth, I've transplanted those graphics to an expanded, clean rom and made a new patch which should apply cleanly to the NoIntro rom. You can download it here
. Hopefully Gideon doesn't mind me tinkering with his stuff.
Disclaimer: this is not endorsed by Aeon Genesis and not thoroughly tested (though I'm reasonably confident it should work flawlessly), use at your own risk. The patch does NOT re-add the splash screen.