I don't think anyone from any culture should be under pressure to marry anyone.
I can understand people choosing to marry within their own religion or belief system. As an atheist, I would never have chosen to marry a devout Christian or a devout Muslim etc, because our priorities simply wouldn't have been compatible. Likewise, while I have greatly valued the benefits of being married to someone from a very different culture from my own, I do understand why some people might choose to marry someone from their own culture, with rituals and traditions that are very similar to their own. I don't think wanting this is racist.
I can also understand why some parents might hope that their children will continue to practise a particular religion or follow particular traditions etc, if their religion and traditions are important to them. They may believe that their children's lives will be easier with these things in common, or they may just hope to see their grandchildren following the same traditions and rituals etc. Again, I don't think that's inherently racist.
However, I do think that parents from all cultures and ethnicities should respect the choices made by their children and accept it if their children choose to follow a different path. And if parents refuse to accept a chosen partner simply because they happen to be of a different ethnicity, then yes, I think that's racist.
I am afraid I don't know enough about traveller culture to be able to comment specifically on their "taboos".