This is just my opinion, but I have built custom synth cabs, guitar cabs, and even dabbled in bass cabs a bit.
I could see a bass cab being used for synth, but think most synth cabs would be likely to fartout on electric bass, whose transients are very demanding of excursion. Traditional electric guitar is its own thing, calling for cabs with a very specific type of tone profile (distinctly non-flat frequency response curve), and drivers that are meant to be driven into distortion, which generally wouldn't work so well for the other two. Now as will33 mentioned, if you use a modelling amp for guitar, that means you want a flat-response fullrange (FRFR) cab, and so theoretically the same cab could indeed work for all three, as the desired characteristics would not be mutually exclusive.