Yes, relaxation is important. It is crucial to use an efficient finger action to execute repeated notes with speed (keep the fingers as close to the keys as you can).
I have found it helpful in pieces with repeated notes (mainly Liszt's second Hungarian Rhapsody and La Campanella), to pick a few beats (or measures) and just work on speed and evenness in the repetition. It takes a lot of work!
As with difficult patterns, it may help to practice repeated notes in rythms.
For example, try practicing groups of two notes, one long and the other very short. Then, increase the number of notes. I have found that groups of four notes work best for me.
I hope this helps...