Yada yada... The age old issue of using a guitar amp for bass comes down to these things.
How loud is loud?
How hard to you play (not the same as volume!)
What do you want to sound like?
I used a very early version of the '59 Bassman Reissue one day. It sounded great. BUT, I was playing my VS '62 P with LaBella flats, we were jamming on some Muddy Waters and Howlin' Wolf songs, there was no drummer, and we were playing quietly enough that we could talk in normal conversational tones OVER the volume.
Even at that volume, had I been playing with an agressive attack, or slapping/popping, it would have been too much for the unsupported speakers in that open back cabinet. And if I'd wanted a more full range sound, it wouldn't have been up to the task- no booming low notes punching through with that rig.
The point is it can work, but most people don't pay enough attention to what the speakers sound like to do it safely. But it can work. Lots of Carol Kaye's and Joe Osborn's early recordings were done with Fender Concert amps- essentially a Super Reverb without reverb. "Son Of A Preacher Man" by Dusty Springfield is Tommy Cogbill playing his P through a Twin Reverb with only one speaker (the other speaker was blown so they disconnected it). It can sound very very good.
But, I wouldn't recommend anyone BUY a '59 Bassman RI, a Blues Deville, etc. for bass. Get a real bass amp nowdays.
jte