Kinda spoilery
The Warrior of Light, as you know, gets in as a ward of House Fortemps. Once you get past the first little bit of the MSQ, you can find out from an NPC in the Forgotten Knight that Fortemps has also hired a company of sellswords. The barkeep mentions that his tavern has an entire floor for transients and travelers. Ser Aymeric, at the end of the 2.x MSQ, notes that he's going to actively attempt to open Ishgard up a bit more now that he's seen the power of unity among the city-states. Some of the job quests even have you getting access to Ishgard; the Bard 50 job quest has a member of the Twin Adders arranging entry into Ishgard.
Between all of that and the decree of the Holy See that Ishgard be repaired and the lands of Coerthas reclaimed, it seems fairly clear to me that Ishgard is importing foreign labor to at least some degree, and those who have something to offer the city can arrange access to the city. In my FC, we're currently discussing various means; some of our members are throwing their lot in with an Ishgardian FC to help shore up the city's defenses, while others are basically arranging to trade research with the machinists and the astrologians (but not those Sharlayan "astrologians," surely -- shysters and rogues, they are
).
