Creating raised beds under existing trees can sometimes be harmful to the trees. You can get away with raising slightly, but too much additional top soil and you risk having your trees decline, or even die.

Mature oak and many pine are normally the first two suggested as being suitable for underplanting with rhododendrons and azaleas. I have an ancient pine on my own property, and dont find much in the way of surface rooting, but a few major roots that I work around.
Have you done some digging there to know what you have?

Best is to find planting pockets, and add compost...the more organic material you can get into the soil the happier your azaleas will be. Then mulch well after planting, and renew the mulch as needed. Mulching with something organic will help to keep weeds down, slowly feed the soil, and retain moisture - I mulch all plants under my own pine with compost twice a year.

The bloom times given for azaleas are approximate depending on your particular climate, I wouldn't be the one to try to tell you specific plants to buy not knowing your location or color preferences. Most nursery identify bloom time of their azaleas as early, mid, late so you should find that information when you start shopping.

Here is a link that might be useful: parital list bloom times

What azaleas really like is high shade, which means only part shade and not a lot of it. In a forest of pine, you don't find anything growing in the understory. That tells us something. Azaleas love pine needles as mulch and a very open forest with no root competition. Azaleas have very shallow roots so won't compete favorably with trees with surface roots. In general, Fred Galle's book "Azaleas" is the basic reference on Azaleas. The ortho book "All About Azaleas, Camelias, and Rhododendrons" has all the basic information in a concise format. The American Azalea Society website is a good resource. Also, catalogues from nurseries are usually very helpful. The best plants are field grown. Container plants will take a while to get accustomed to planting in real soil.

Here is a link that might be useful: American Azalea Society

Thanks for the responses. I actually looked at the area today and the root system isn't as bad as I had remembered. I think that I do have some pockets I can work with. If I plant in the next week or so, can I expect blooms this year?

Possibly, if you buy blooming sized plants already in bud (azaleas will have set their flower buds late last summer in the nursery for this Springs flowers).

Not to the same extent as large leafed rhododendrons, but it wouldn't be unusual for newly planted azaleas to not bloom fully their first year (even two) after planting...they'll be establishing their root systems and adding to their framework in place of setting flower buds. You may not even notice with azaleas that they haven't bloomed to their full potential....

Are you in zone 8 in the south? If you have mature pines and the azaleas will have dappled shade, they should be fine.

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Azaleas are typically planted here in bud and bloom in the spring and go on to make a show, even small plants.

Nell