You mean like the Dutch stadholders were counts of Nassau, or used to be counts of Lingen an dukes(?) of Moers? Yeah, that could happen and did happen.
There is something I forgot to mention. When speaking about Dutch stadholders and personal unions you should never forget that a stadholder is not a king. The Dutch stadholder often was one of the most influential people in the Netherlands (although often he wasn't), he did not rule the country. Actualy the early stadholders, including William III of England, weren't even stadholder of all Dutch provinces. Friesland and Groningen had, at first, a different stadholder than the other 5 provinces. Also the office of stadholder wasn't heriditary, at least until 1747. When William III died without children the ruler of Prussia was his closest male relative and inherited Lingen and Moers. He did not become (or could ever become) the Dutch stadholder. William III wanted the Frisian stadholder to become his successor. He did not. The province of Holland decided they didn't need a stadholder, so they and 3 other provinces didnt have a stadholder for 45 years.
So, creating a personal union with the Republic of the Netherlands is hard. Even the ANglo-Dutch personal union never was a true personal union.