There were numerous Gedolim who’s wives didn’t cover their hair. That much isn’t really up for debate, however context is crucial. The lived in very different times were Jewish girls weren’t educated like they are nowadays. There simply weren’t many options in regards to Shidduchim. It’s no wonder several Gedolei Yisrael from Europe got married much later in life- their simply didn’t exist a plethora of prospects looking for those types of guys back then. However, nowadays things have very clearly changed.
I still, however, harbor sensitivities to people being too picky. Many “older” guys you find nowadays are completely transfixed by the prospect of marrying the “perfect” girl- a girl who doesn’t exist in reality. That’s definitely a problem and something which everyone in dating needs to do a serious cheshbon about. The OP’s question, however, is about dating someone who doesn’t exist within the same stratosphere as the bochur. Such a vast difference in Levush (pants vs black hat) is usually indicative of a completely different perspective about life and the role Judaism should play in it. Although a Shidduch is technically possible, its akin to setting up two people who don’t speak the same language; it could work, but you have to be a little nuts to suggest the shidduch