Using a CF or SD to SCSI adaptor does not change it's appearance. It is a functional SE\30. It will even function better than before. Where's why:
1) - Hard drives over 500MB tend to run hotter than the original drive that were in there in 1988. A lot hotter.
2) - Hard drives over 500MB takes more current to run as they spin faster. This adds to the strain of the SE\30 Power Supply.
This means that the SE\30 will have a shorter life, even if you recapped your logic board, your analog board will suffer the most.
Another point to think about is where are you going to get such a drive? Drives of these sizes are no longer made. In fact anything under 50GB is no longer being made. So much of the drives you will find are NOS Drives - NOS being "New Old Stock" or stock drives that did not sell and put into storage. on some shelf somewhere. So they are New-Unused drives. But there are several problems with that.
1) Head/Platter Stiction. Sitting around not spinning, the heads will get stuck to the platters. It's not of matter that it did or didn't, It's a matter of When they did or when they will.
2) The lubrication on the bearings (on the platter spindles and the heads' axle) would have deteriorated to either a mushy gel, a crystalline solid that will shatter to a fine dust inside the drive when the bearings break free. At this point the bearings will be nothing more than metal on metal and they will quickly wear out.
And how do you know that these drive are "New"? It is not like they have a digital Odometer on them. You can not tell without ripping them apart and microscopically analyzing the parts for minute wear. I can do that - give me a 1/2 million lab to figure it out! But chances are you will be getting a used drive that somebody probably ripped part at one time or another, you wont be able to tell if they did. It will definitely have "high mileage" on it and doomed to failure at "Who knows when."
Though a CF or SD to SCSI adapter is not cheap, averaging $150 on ebay, CF and SD cards are fairly cheap. You want something under a GIG, it would be around $10. And you can get new CF card from 32megs to 4GB and a new SD Cad from 1GB to 4GB as they are still being made.
Since a CD or SD to SCSI adapter and card is electronic and has no moving parts, it takes very little power to run it. They do not heat up. They do no stress out your power supply or analog boards. So your SE\30 will definitely last longer. And it will run faster as there is no buffers or signals to process mechanically.
Personally, I have a SE\30 and a Classic II I'm saving for a CF to SCSI adapter. The drives in them are older than the younger members of this forum, so I know that it is a matter of time as to when they will fail, not if. The same with my other Macs (you can see my list below), starting with my Mac IIci with the 040 Daystar Accelerator. That machine I originally hacked to have 2 hard drives!
But the choice is yours.