I see no indication that Gale knew the Germans. Perhaps it is Madrigal that connected Gus with both Gale and the engineers? Maybe Lydia in particular?
How Gale came to work for Fring is explained in the show(s):
In 1994, after moving to the United States, Gustavo Fring established a college scholarship, known as the Max Arciniega Chemistry Scholarship, at the University of New Mexico Chemistry department. This scholarship honored Gustavo's closest friend, Maximino Arciniega. Gale was a recipient of the scholarship (perhaps one of three dozen), and this paid for his education ("Hermanos"). While at UNM, Gale received his Bachelor's degree, and graduated in 1999 ("Hermanos"). Gale had been pursuing his doctorate at the University of Colorado under an NSF grant but realized that it was not the life for him because he loves being in the lab and wanted to preserve the 'magic' he saw in chemistry. ("Sunset")
After Juan Bolsa instructs him to find a drug supplier north of the border, Gus visits Gale's chemistry lab on the UNM campus. Gale presents Gus with a hidden case containing methamphetamine vials of varying chemical purity. Dismissing the samples as "dreck," Gale urges Gus to allow him to produce higher-grade meth in his lab. Gus politely declines, saying such action is not needed yet and that Gale is meant for "better things."("Something Beautiful")
Gus later appears to change his mind and hires Gale as his meth cook and Gale visits the excavation underneath Lavanderia Brillante. Gale is excited at the prospect of cooking in what will become a meth superlab, but Gus stresses that he won't begin work until the lab is complete ("Winner").