Not only chassideshe “royals” but all royals inter-bred (look at english royal history specifically)
Uncles marrying nieces, as strange as it may seem is/was actually encouraged by the mishna and halacha (bas gilo)
Medically speaking, as was pointed out, if nothing shows up to be a problem then why not? True you may be narrowing the gene pool so it wouldn’t be recommended for everyone to be running around rampant marrying their first cousins but I don’t see it as an issue
On the other hand if it is a cousin one knows so yeah it may seem awkward (someone tried setting me up with a second cousin of mine and well let us just say that I am happy she never heard about it (when I was in high school I used to be by their house almost all the time)
😀 Zuberman! 😀