Is it always the classical tradition (a la Hanon) to use the 4th finger when on a black keys and the 5th finger when on a white keys when practicing octaves with the right hand through all 12 major scales?

Same things also for triad arpeggios with right handed octaves (4/black, 5/white)?

I am curious to read the answer(s) too, so let's not let this slip off the radar screen.

John? Peter? Gary? AZN?

Depends on the student I think.

I've played (and taught) octave passages using only 1/5 and also using 1/4 and even 1/3 (I've got reasonably big hands). However I find that I tire more easily when I use 4 (or 3), so I generally stick to 1/5 for all octave passages now.

The proponents of the Taubman approach would advise against anything but 1/5 for octaves as other fingerings force your wrist to turn outwards in an unnatural position. I think that's why I was tiring and getting sore when doing extended octave passages.

I think the key is to relax the hand in between each octave. It's the constant stretching that adds tension (but I do like the variety of 1-4 and 1-3 to the 1-5).

Yes. Relaxing the hand is very important.