Hi,
Theortically, you can use any amp for anything, after you got the input signal level to be compatible. (ie. mic level, line level, instrument level..etc)
Except you MUST know the LIMIT of the amp, mainly by feel firstly. Bass & guitar level are similar, thus you can interchange, BUT the guitar amp is built to output more of a certain range of frequency, it's what we call voicing.
The guitar amp is voiced more to the mid range, so you might need to reduce the mids and boost the lows on the EQ adjustments. Remember to cut out the REVERB, bass sound bad with reverb, it prefers chorus.
If you are recording by mic, I don't think you will crank the amp over the limit. So should be relatively safe. This is because bass signal needs more power to generate the sound, thus you amp (especially the speakers) will be heavily or overloaded if you crank it to keep up with the other guitars on a live set.
Also, bass amps are closed back with tuned port cabinet, so as to achieve the desired low end bass sound with less power needed (better efficiency). Guitar amp mostly are open backed, so the bass response or efficiency is much lower.
Just a small history lesson, when fender produced their Bassman Amp more than 50 yrs ago, guitarist find it so useful that it was used more as a guitar amp than a bass amp. Of course the bassman was built well and is suited for both tasks.
Mike
(Amp repairer)
Mikemann Music Studio
www.geocities.com/mikemann88