Alot of the time when playing reggae, you want to think of the bassline as another melody as well. Don't think just harmonic support, think it's own kind singable tune. But generally if you want to get into chord scales it's mostly diatonic, and very very rarely playing anything more complicated then a dom7 chord (root 3rd 5th b7th).
If you were going to be taking a solo, i'd stick witht he key centre. If the tune is going Amin to G, then you are looking at a ii to I chord progression. so A dorian, and Gmaj, which are both the same scale (basically).
Try to stop thinking tho. Just keep it diatonic and it will be fine. blues scales tend to work, but from a bass point of view, don't solo? I ahve a friend who alwayus says "no room for bass solo's in reggae music" and to an extent he's right. But i played a pretty decent one on my reggae bands myspace
http://www.myspace.com/skillshinedubs . The chord progression is Bmin and Emin occasionally going to that V chord with an F#7. My solo is pretty diatonic (and occurs after the bridge, which is more diatonic chords in Bmin). I remember thinking it was lame and not my best work but after repeated listening i think it fit the tune better then the "jazzier" solos I did on other takes.