The Andorians did have a defense fleet when they were in the Federation. Paths of Disharmony said that half the fleet was destroyed in combat against the Borg, the Therin presumably belonging to the half of the fleet that survived.
Wasn't that a Strafleet defense fleet?
And don't forget that at one point in FG Riker does say that it appears the Andorians are basing their military stuff on their pre-Federation days. So it doesn't sound like Andor had a separate space fleet during its Federation days.