I think that
The krynn can do that, its said they can trade while at war in their tech tree.
The Krynn can trade with other civilizations while at war however I do not believe that they can open a trade root lets say between the Altarians and the Drengins. If trade ships going on my worlds are attacked because I am at war, I should have a way to make money with a trade route which does not involve my planets directly.
I'm also thinking along the lines of the days of Piracy in the 1500's - 1780's. A captain who could net set anchor in a port because his nationality was at war with the nation of that port could sometimes sail in the port anyways by using a captured ship of another nationality and flying that flag. In modern terms, the captain was using that ship as a proxy server to make himself look like he was from another nationality.
Come to think of it, if we take games like: "High Seas Trader" and "Microprose Pirates", we had a ship which could spot lucrative trade of specific goods between two or 3 colonies and a captain could make money from purchasing one product cheap on one colony for example guns and sell it to another colony which needed it because of circonstances (for example pirate attacks).
A civilization under pressure ei making payments to the Drengin may like to trade for supplies which would help their situation or be inclined to share any information on the Drengin with other civilization hoping to weaken them.