The problem is general and does not only apply to graduate school application.
It really depends how the interaction with "fringe" topics occur. If you are negatively inclined (skeptic blog) or sarcastic (CAUTION:Poes's Law), you will very likely experience no problems, the worst will be that some people scold you for wasting your time.
The most common, I would even say reliable, occurence that you will encounter in the open is a pet theory. Almost every scientist has one, these theories are stroked and caressed and their range is unpredictable. It could be inside or outside of a subject's area, from a curio to outright bizarre.
If you, on the other hand, are genuinely interested in a fringe topic generally and communicate so, you will very likely experience that your reputation goes down very quickly, especially in STEM fields. In contrast to their projected image to the public (openness to inquiry) scientists at large are acting within their community mostly intolerant to fringe topics. A person outside academia asking about a fringe topic may be tolerated, but for fellows the patience is very thin.
The worst thing you can do is engage in a public hot topic on the wrong side. Academic people may forgive your interest in an arcane topic like panspermia, but defending creationism or parapsychology (even if you only correct a false argument from a skeptic) paints a very big red cross hair on your chest. It is not a wise thing to do.
You may have noted that I said "acting". It is a curious phenomenon that actually many scientists have interest in fringe topics, have experienced something strange or, God forbid, do believe that something may be partly true.
The thing is that there are..."guardians". These are people from academia which have (surprise) no pet theory and which are glad to have finally found the pristine area of knowledge and truth in science. They also want that their peers share their enthusiasm of defending science against the common enemy. Their worldview about the non-occurence of fringe topic beliefs in academia is quite rosy because they do not realize that their enthusiasm prevent people from telling them what they really think.
People may believe that this cannot be true but there are strong indicators because it happens at very high levels: Newton was very interested in alchemy and theology, Wolfgang Pauli was interested in parapsychology, David Deutsch embraces the possibility of time travel.
If people get the impression that you don't rip off their heads or laugh at them, they are much more open in private. So I would recommend to abstain from dabbling with fringe topics in public and use private communication channels if you have interest in them (choose your counterpart wisely).