There is always such a possibility. I like IEO's and trust them more than ICO's, but only if IEO is conducted on trusted exchange, for example Binance. But even then you can be scammed, as no one can guarantee you that this or that project isn't a scam. Everything can happen, even on a major exchange.
low rated exchange usually have nothing to lose when it comes to reputation so they usually could turn out to be a scam or the project itself is a shitty project that usually being dumped after the funding.
If it's the major exchange they will definitely put their project into consideration whether it will make their reputation bad or not. major exchange always put the reputation above anything else and if there's only one project that turn into a scam or becoming a garbage project they will definitely lost a lot.