Yes, the iPod can play AIFFs.
Just to be clear: You used Audio Hijack or a similar app to record the output of Realplayer as an AIFF, yes?
You would then:
1. Add the AIFFs to iTunes (drag & drop)
2. Optionally, select Advanced: Convert Selection to mp3 (or AAC if that's your default import setting)
3. Transfer the AIFF or mp3 or both to your iPod like any other song.
That sequence should work...