For this reason I would never do it, period. Yes, you can get away with it, esp. if there is no OS drive or whatever on the channel, but if you plug&unplug SCSI often (sometimes 100s of times in a week) and you are not in Centronics world sooner or later you will mis-seat a cable. This will nearly always ruin the cable, may ruin the connector on the SCSI device, and if powered can cause rapid nastiness. OTOH, in a well equipped shop if the power is OFF this is not a huge deal - toss the cable in the NFG cable pile, scowl at going through $1000s in cables every year (SCSI, VGA, RGBHS, RGB, XLR, etc.), check the connector, be more careful....
In fact, it is sometimes possible to mis-align a 68 pin SCSI cable and not realize it until powered up, which is why I always double-check.
A tape drive on its own card may be an exception to this, but why chance it?
As to the screws, my eyes are too aged these days to be able to always tell, so I always line up some "usual suspects" and lightly test by hand straight into the drive. If the screw goes in easily like that, then I know I am good. OTOH, on one or two occasions I have deliberately used screws that were too big due to a need to hang a drive in a particular, unusual way (kiosk or whatever). Big screws sometimes seem like the only way to really mash a drive in, though this is probably not recommended for long-term use.