[...] the picture you see above, you can see the RAM Disk mounted

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Well, I think that picture delivers a different information. A better one, in fact. It shows that LIDO can access the SCSI bus and it shows SCSI device #7, that is the Macintosh on-board SCSI controller. The RAM Disk is not implemented as a SCSI device, IMHO.

Maybe it's the connector. Sure would be a lame way to ruin a party. Even if the HDD cannot present a valid boot folder, that's still no excuse not to be detected.

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But if the SCSI cable between main board and hard disk is broken, that would be an excuse, wouldn't it?

I have a 50 pin internal SCSI cable on the way from eBay.

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Certainly a good idea.

Any idea why this machine won't boot from System 7.5 Network Access Disk? (Blessed folder and all)

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Since you have successfully booted w/ 6.0.8 from that floppy drive, we can assume that the drive is O.K. Have you ever booted another Macintosh w/ that 7.5 Network Access Disk? Can we assume that the 7.5 NAD is not defective? Just an idea.
The 6.0.8 floppy you have used to boot up the SE/30 is a 1.4MB diskette, isn't it?