#1
My brother plays guitar and has quite a few pedals. If I tried some of them out on my bass, mainly a Boss Phase Shifter and a Behringer Ultra Octave, would it harm the pedals in the same way it would harm an amp, or would it be okay and just not work as well as a bass pedal?
#2
It's alright to use guitar pedals for bass. It might not sound any good, but then again it might be great.

The actual signal doesn't do anything to pedals or amps. It's the speakers in amps that take the punishment since guitar amp speakers can't handle low end at high volumes.
"You can practice to attain knowledge, but you can't practice to attain wisdom." - Herbie Hancock
#4
I just noticed one of the pedals is an octaver. Don't use an octave down, it might damage your speaker. At least at high volumes or for a long period of use it might ,so be carefull with that.
"You can practice to attain knowledge, but you can't practice to attain wisdom." - Herbie Hancock