Azalea trees can generate on icebergs when there is a lush caves biome under a (deep) frozen ocean biome.

An example can be found in a world with seed 42 (yes, it is my test seed) around -120;-240. The tree isn't always at the same position and might be not generated at all, so you may have to try a few times.

I saw the MC-238499 resolution stating that azaleas can be generated in any biome and I'm okay with that for ground biomes, but I'm not sure it is relevant for oceans.