With Steve DeBeste working out all the "what the?" aspects of the Vandread timeline and world, lemme toss my hat into the ring with two possible answers to two of his questions-how did the Pirates get ahold of serious military ordanance and why is B.C. with the Pirates and why does she (heh) not warn the Tarek government of the Pirate attack?
The last question is the easiest, but requires the first. Be warned, there are spoilers if you haven't watched the series.
To figure this one out, let's allow for the following two cheats-a faction of the Mejale have access to a bit of the Blue Paksis, enough that the Blue can occasionally generate "hints", that help the Mejale government keep on top of the Tareks. And cheat #2 is that this faction is not the one in power at the time, or was dismissed by the time the Nirvana returned to Mejale.
The Blue builds up a reputation for providing useful hints, and one day, it suggests that there's a major threat coming, outside of the Mejale/Tarek system. The problem is, the system is so insular that there is no real trade or contact outside...except for pirates disposing of their loot. So, the faction needs it's own "pirates"-building up it's reputation for piracy, so it can make contact with other pirate and less-than-legal factions outside of the Mejale/Tarek system. They're equiped with Mejale military ordanance, probably in secret or via quasi-legal "transfers", and a ship or two. Probably the senior officers, Captain and Gascogne knew about the plan, and there might have been sealed orders in the safe for B.C. if "something went wrong".
The raid we saw in the first episode of Vandread was pretty much a combination of gathering a big enough stake to really strike out into deep space for information and a live-fire training exercise to really get the crew ready for operations. Which, of course, the Blue Paksis wanted in the first place...
Second question...why is B.C. with the pirates (considering her high-to-extreme competence) and how come she didn't warn Tarek of the upcoming pirate attack? That's easy-B.C.'s spy network (she probably is a master spy, not a spy-master...gathering info from agents, as well as her own) reported that a group of pirates was being very, very well-armed. And, they were being very mysterious about their plans for all the gear and loot disposal. There was other bits and info...a chart request by an assistant astrogator that would be only used for somebody navigating beyond the Red Line. Gathering items that would only be used for trade outside of the system. All of which most pirates normally wouldn't use...or, if so, in small quantities.
B.C. has been described as "one of the elite"-and could write her own ticket. Even if the Captain suspected her, B.C.'s talents and capabilites meant that she had to hire B.C., to keep up her pretense of being a pirate. And, her competence meant that she could be easily promoted to XO. Which would have given her access to planning and preparation info for the Tarek raid.
The problem is timing, and how quickly the message can be sent. Considering there is no real contact between Tarek and Mejale, the messages have to be sent by some form of dead-drop mechanism. Odds are, it was via a tight-beam laser to a recording system, then picked up by a Tarek ship. By the time that the message gets to Tarek about the raid, the message would have gotten there just enough prior to the attack that the response would have been...noticeable (and possibly tipped off the Pirates that there was a leak), during the attack (which could have been compromised by the Pirates if they captured the ship), or after (which would have been politically compromising...). Considering how competent B.C. is, Tarek Intellegence would have understood-and realized that ending the raid without another contact would have risked their deepest agent in the fleet.
This is the dance of intellegence that gives good spy masters and master spies headaches, ulcers, and grey hair.