I mean, I found it in two pretty substantial dictionaries after a quick search: https://www.dictionary.com/browse/sike https://www.oed.com/search/dictionary/?scope=Entries&q=sike
Along with countless other dictionaries that cover slang and alternate spellings, but I figured you wouldn’t think that those counted.
But I will say that if being in a dictionary is a requirement for a word being part of the English language, you’re not accounting for a large portion of modern American/Internet vernacular. People who actually study language would never have this take, as languages are made up of the words people actually use, not the words that a board of folks decide to put into a list.