Leaders expansions: Is trade commerce allowed during Recruitment phase
Tl;dr: Yes.
A strict reading of the rules would imply that commerce isn't allowed for wonder construction even in the base game:

Throughout all 3 ages in a game, the players will get to build structures (cards) and Wonders (board).

...

Commerce
Often, a player will want to build a structure requiring resources he or
she does not produce.
If these resources are produced by a neighboring city...

However, the game designer has explicitly stated that you are allowed to use commerce for wonder stages. Given that clarification, it is reasonable to assume that when the Leaders rules are once again ambiguous on the matter, you can again use commerce for wonder stages there too.