Most Polyurethane paint systems rely upon chemical bonding, not mechanical, between the primer and the single stage paint coat. They typically give a max time window between THEIR primer application and the top coat application to allow this chemical bond.
The rustoleum primer WILL NOT chemically bond to the PPG S/S paint (no isocyanates in rustoleum paint), so you will need to mechanically abrade the primer for decent bonding.
I am fairly certain that if you call PPG, they will NOT approve the application of their SS paint over rustoleum primer, though they will likely be ok applying their epoxy primer over it, if it is cleaned and scuffed first. They will likely tell you that you can save the extra step, as their primer will adhere better to the aluminum than the rustoleum will.
Most Epoxy primers are now direct to metal approved and many will not allow that primer to be applied over previously applied self-etch primers, as they have found adhesion issues in these cases.
Not saying rustoleum self-etch primer is bad, only that it is not compatible with direct application of P/U S/S paints. You have to decide if potential delamination between the primer and color coat is a problem for the small part you are contemplating. If the parts are well hidden, this may not be a problem for you.
Larry