Will galvanized metal conduit balusters resist rust?
Rigid conduit (which is pretty much the same thing as galvanized steel pipe) is galvanized with a considerably thicker layer than EMT - it's also stronger (emt is a bit flimsy for a railing) and more expensive (such is life.)  Since you didn't specify what type of galvanized metal conduit you were considering using, what happens will vary with the type you choose. 


EMT is very flimsy and prone to rust - inexpensive and easy to work
with, but not a great railing material, IMHO.
Rigid would work nicely, and probably not rust for a good long time if the galvanizing was not deeply scratched.
I know there is a third product (IMC) but I don't have any direct
experience with it. I believe it's "Intermediate" Metallic Conduit
and heavier than EMT, lighter than rigid - and I don't know how its
galvanizing compares.