[@Jangel13] It could be done exclusively as well, with the worship of the one being abandoned.  However, what I had in mind was how common it is for different people in the same religious group to be drawn to distinct spiritual methods.  Everyone is trying to get to the same place but they all try different paths, to one extent or another.  In this case, the viability of this approach seems to lean on these questions.  How jealous are these deities?  Are they opposed and in conflict, indifferent and parallel, or allied using their differing specialties for a combined goal?  And, as things stand, I am not the one who can answer these questions.

So, if the particular nuances of dual worship strike you as being incompatible with your world then that is a thing that would have to be changed somehow.