You may be interested in this earlier answer I wrote, on Polka and its influence on Mexican norteño music. In short: Yes the influence of Polka on some Latin American regions comes through migration from Eastern Europe and modern-day Germany. But this migration started much earlier than WW2, already in the early- to mid-19th century. Adding two relevant parts from that answer:

"The large-scale migration of German, Polish and Czech people in the 19th c. especially to Texas and Nuevo Leon would have a major impact on the musical development. As an example, a large migration of Germans to Southern Texas took place in the 1830s and 1840s. They would make up the largest ethnic group in Texas of European descent, and by 1850 Germans made up more than 5 percent of the entire population of Texas (this region becoming known as the "German Belt")."

...

"Towards the mid 19th century, Iberian dances lost polularity rapidly, surely in connection with the wars of independence and the anti-Spanish sentiments they brought. At the same time, the polka and other European musical styles spread throughout the whole American continent. Another example of this would be Argentinia, where polka can be traced to at least 1845, and where the accordion would of course also play in important role in genres like the tango. Santana Garza mentions how from the late 1840s there kicked off a veritable polka "craze" (furor) in Mexico, with the word being used for a certain type of male pants, and at one moment polkos even being applied to all things "strange and extravagant" (crazy how word meanings have changed).."