I’m not sure, but I don’t think Casinocrush is saying that he’s currently having complaints from players that are having multiple account problems here. I think he’s asking you as a precautionary measure.
People are posting no deposit bonus codes on the forums and the same code that will work at Silver Oaks, will also work at some or all of the casinos he mentioned.
Because the same free chip coupon that works at Silver Oak, will work at the other casinos he mentioned, I think he’s concerned that these casinos aren’t completely unique and individual casinos, but rather are whitelabels or skins of one casino. In which case players COULD end up with multiple accounts not knowing they’re doing so.