Everything from the location to your planting sounds just right. Soft new growth often tends to wilt until it has had a chance to mature. It is possible, however, that the root ball has dried out despite the fact that you soaked it before planting. Water with just a slight trickle fom the hose at the base of the plant. What you want to do is get water into the root ball without saturating the surrounding soil. Digging up the root ball to check it is also a good idea. Roughing up the root mass often needs to be more than just a little. You want to eliminate circling roots and expose root ends.

Album, btw, just means "white". It does not indicate a particular rhododendron variety. Catawbiense album is commonly available and is a hardy, adaptable choice. No fertilizer is necessary or desireable unless a need is indicated by a soil test in the first year of planting.

Since you planted it amongst those very competitive oak roots, I suggest that you should be watering that root ball every single day. Don't cover the very top of the roots with mulch and concentrate your watering just to that area. You won't need a lot of water.

It's been proven that woody plants acclimate and become fully established much faster if watered frequently. And when planted in a location where there is an established root system, the watering is all the more important.

Oaks and most other trees concentrate their primary root development in the top ten or so inches of soil. That's where the essential fibrous, water absorbing roots live. It's not surprising that your azalea is wilting.

Again, provide water just to the root ball, slowly and frequently to insure infiltration.