I have an obvious alignment issue and I need to replace the front 2 tires because of the wear that it has caused. One of my rear tires is brand new (replaced a matter of weeks ago), but the other has maybe 40% tread on it. Do I need to replace that one before I have the vehicle realigned?
You can have an alignment done at any time - with or without replacing tires.
But it is worth getting an alignment done so the new tires last as they should.
Edit: even if the rear is a solid axle, an alignment will show if it is bent and needs replacing / repairing depending on its construction.