So any of those Pokemon have a Classic Ribbon or a Premier Ribbon? If so, then you will be unable to trade any and all Pokemon possessing such ribbon. All event Pokemon possess either the Classic Ribbon or the Premier Ribbon.
While event Pokemon cannot be put into the GTS, they can in fact be deposited on Wonder Trade and can be Link Traded.
Source: Experience (Traded event Deoxys to passerby in X for another legendary I can't remember); here
Hope this helps!