It is possible, and you may find examples in various sources showing machine tooling centers used as two datum features for establishing one datum axis. The caveat is that you have to make sure that the cone angle of the true geometric counterpart / datum feature simulator machine centers is unambiguous*. The examples do not address that, not even in the ASME Y14.8 (Castings, Forgings, and Molded Parts) standard referenced above by powerhound.
*It is only unambiguous when it's basic on the drawing. If it's X.XX°+/-0.XX° then it is ambiguous unless you explicitly specify the angle of the true geometric counterpart.
