In a sense, the Fatches Family could be considered to have 'brought in capital to join the group'; they were originally the masters of the Three Worlds of Fatches and were willing to pledge full allegiance, bringing help with them, so the Empire recognized and legalized their rule.
This is what is called the 'historical factor'.
In short, there are all sorts of entirely different situations within the Empire that all require special handling, so there are corresponding loopholes left in place.
However, such a situation is relatively rare; normally, the Empire would not approve the establishment of a cross-stellar cooperation organization.
At least, there was no chance for Gu Hang to obtain this on his own.
Mainly because he had no 'friends' at the higher levels of government in the Central Empire, even if he wanted to engage in some sort of beneficial exchange, he simply had no access.