A RedBear head is 100% legit on bass for Stoner Rock and Doom Metal. People have even used stock Marshall and Orange heads for this use case.
The RedBears have extended bass into bass amp territory, so they perform this task even better.
Using the same head for guitar and bass goes all the way back to the birth of the genre of Doom metal with Iommi and Geezer sharing the same Laney amp head.
It creates a unified tone, and Doom bass is often distorted anyway so you don't have to worry about the amp breaking up too early. Many Doom bassists will even use fuzz pedals which are way more clipped than a RedBear will ever get, so don't stress about the distortion if Doom is the use case (which is what these bassy gainier 800's excel at imho).
You could put a bass pre like a Tone Hammer pedal up front (or in the loop if you have an MKE) for even more tone shaping options (and set the amp flat / mid and treble at 12 O'clock or below and bass dimed, with the pre / gain dialed back).
I have a RedBear MK60, I play a P Bass through it and an SG on (non bass) lead / rhythm (well, Riff, really for Doom). It is a totally 110% valid as a Doom amp for bass, for that particular use case is absolutely rips! On the low input it essentially is a Stoner / Doom bass amp.