Pirate musician entertaining the crew...
Pirates came from all nationalities and background, but during the golden age of piracy, most were Welsh. There were many Irish and English pirates, few Scots. French and Spanish pirateering was widespread. There were also a lot of runaway black slaves, know as "Cimarron" (Spanish for maroon), and there were several famous black pirates, such as Diego Grillo and Lauren de Graff.
Pirates recruited crews both on land and at sea. On land, a pirate captain would let it be known that his ship was "going on the account", and those interested in joining would sign on voluntarily. Their decision would be based on the reputation of the captain; if he was a man renowned for returning from his excursions with rich pickings, he would have no shortage of willing volunteers. Recruits had to bring their own weapons: at the very least a pistol, black powder and shot, and a sword. Men with additional weapons were in demand Shipmates who were musicians, or who had skills such as carpentry and cooperage, were even more desirable, and were often seized by pirates and forced to join the crew.
At sea, men were recruited from seized ships. Whenever pirates took control of a ship, the common sailors were given the choice of joining. Any who did so immediately became marked men, but at least they escaped the harsh naval or merchant life for the promise of riches and greater personal freedom. However, many sailors made it appear as if they were being taken against their will, so if caught by authorities at a later date, they could plead innocence. They were made to sign "shipboard articles of conduct", a set of pirate rules. This document could also be presented to prove coercion.
Carpenter, J.R. (2006), Pirates, Scourge of the Seas, pgs 46-47;
Barnes & Noble [Gusto:China]
Steampunk Airship Pilot (by Mr.Xgabe, conceptart.org)
Steampunk Implications: Well, many of the people in the sub-genre (Steampunk / Sky Pirates) have both male and female individuals manning the ship, so an argument could be made for either sex joining a piratical crew. Nationality may not be an issue (rl or sl), but absconding with persons of useful skills (e.g. physicians, damage control persons, engineering rates, ect...) would make perfect sense, and translate over directly.