No you can not directly attack anything with them. However, at the farthest that I have gotten before winning in the game the stats of the military starbase were like:
26 26 26 (B / M / MD)
15 15 15 (BD / MD / MDD)
As well as:
+5 to your ships attacks in the starbases sphere of influence.
+1 speed to your ships " "
+10 defense to your ships " "
Add that up to a medium ships with pulse lasers and mass drivers that are possibly second generation so you have at best a 4 to 6 in either category with minimal defenses you get a pretty damn good set of odds on your side when an other than good intent civ tries to take you out or... if your like me, just before you go and take them out set up a couple in their area with a mass constructor attack! (yes I know, they cannot attack but boy, when you build a military starbase in their area they get pissed and try to take it out instead of taking you on.)
Good hunting, until we meet that is.
W/R
Suralle Straykat
Kat Lord @ Large