Not sure I fully understand what's going on with this, but if you're using a Oneworld Explorer (and, I think, Global Explorer) RTW ticket, you are limited to the Oneworld carriers, codeshares where both the operated and selling carrier are Oneworld members or select other carriers that operate as regional affiliates or franchise carriers for a Oneworld member. You cannot on a OWE fly United from Chicago to Hong Kong, for example.

Perhaps your TA is talking about another RTW which might mix and match carriers from different alliances. But, if it is a Oneworld RTW product, your travel will be limited to the Oneworld carriers.