In terms of piracy the problem for a pirate in the Traveller is that you HAVE to operate close to your base. I mean, suppose you have a 'hot' ship, Jump 3! OK, you can maybe cover several systems, but you constantly need to refuel, certainly after every jump. You can do it way out the back of beyond at some smelly gas giant, but the fact is, the Navy is going to pretty soon know that your base is in a certain volume of space. If its extensive enough to service ships, then there must be SOME way to supply it, so its location cannot remain perfectly hidden.
So, I'd posit that pirates may exist in areas where there is 'red' territory within Jump 2 or so such that the Navy can't go there. They KNOW where the pirates are, certainly within a small region of space, but some other empire, aliens, whatever prevents them from acting on that information. Of course most merchants will just NOT GO THERE! Or they will stick to a few very heavily defended jump points close in to destination worlds.
Basically pirates are going to be stuck going for free traders that are dumb/desperate enough to work routes out in known dangerous space away from patrols and such. Its not much of a living.
Contrast this with the Age of Pirates situation back in the 17th-18th Centuries. A sailing ship of the late 18th Century could easily cross entire oceans without needing to make stops, and there were MANY places to hide and resupply. A ship crew could basically 'live off the land' for years at a time, travel to various parts of the ocean with little chance of being spotted, and then strike. The oceans were also a legal no-man's-land where ships of many competing polities freely sailed. Governments could simply issue letters of Marque & Reprisal to any old Joe with a boat, and they could pretty much go where they wanted. There WERE a few 'pirate bases' in various places at various times and that worked because you could slip out, sail far away from any patrolling warships, and take up your trade.
Piracy actually seems pretty non-viable in the Traveller milieu for basic technological reasons, really. I'm sure it would exist, to a degree, and that might be all that matters for an RPG, but I doubt it would be very prevalent.