Tokens can in fact be used in OQL. They can be used in where statements.
For example. You can call [%CurrentDateTime] in an where statement when you are comparing a date time attribute.
Following this logic, if you have a atribute connected to System.User you should be able to reach the [%CurrentUser].
Such a statement would look something like this:
(StartEntity)_User/System.User/ID = '[%CurrentUser%]'
Tokens like that are only for use in Xpath queries. See documentation here.