Here is the relevant section of the Pennsylvania Department of Transportation regulations that references the reciprocity agreement with Germany (emphasis mine):
WHO NEEDS A PENNSYLVANIA DRIVER’S LICENSE?
• Individuals who possess a valid foreign driver's license from their country are authorized to drive in Pennsylvania for up to one year from their date of entry into the United States, or upon expiration of their foreign license, whichever comes first. International driving permits are strongly recommended, but not required. Reciprocity agreements exist with the countries of France and Germany allowing for the transfer of a valid non-commercial driver’s license without Road or Knowledge testing; however, a Vision Test will be administered. (Transfer of a driver’s license from Puerto Rico, France, or Germany cannot be completed the same day.)
• People living in Pennsylvania who are at least 16 years of age and want to drive a motor vehicle.
• People who just moved into Pennsylvania and are establishing Pennsylvania residency - if you hold a valid driver’s license from another state or Canada, you must get a Pennsylvania driver’s license within 60 days after moving to Pennsylvania and surrender your out-of-state driver’s license.
The first bullet point applies to your circumstances, which makes no mention of having to surrender that license. The third point describes individuals who have a driving license issued by another state in the USA. Additionally, the non-immigrant visa documentation you'll be required to provide supports that you are not relocating permanently.
UPDATE: after Facebook messaging the Pennsylvania Department of Transportation (PennDOT):
If he chooses to have a PA license, he will have to surrender the German license, which will be sent back to the DMV in Germany.
The process is as follows: He would come in with a completed application for PA license. He would then have his German license verified by the German DMV, and have his immigration status verified at the same time – this process can take several weeks, depending on how long it takes Germany to get back to our us with a positive response on his German license.
Once verified, he would be eligible for his PA license, but he would have to surrender his German license at that time, which we would return to the German DMV. Presumably he would be allowed to get that German license back upon his return to Germany.
Please also note, though, that a valid foreign driver’s license is acceptable to drive in PA for one year from the date of your most recent entry, or the expiration of your foreign driving license, whichever ends sooner. The one-year time frame starts anew every time you enter the U.S.
If choosing the second option, [he] could also obtain an International Driving Permit from an issuing entity in Germany. While the IDP is not required in PA, we do recommend it so he could present it in the event of any traffic stop by law enforcement.