is all the black and white footage documentary?

no, we watched this in film class and my professor made a point to mention afterward that all the concentration camp scenes were actual footage. All the camp condition and dead or dying people were real.

Yes. Everything in B&W was from the time it actually happened, either captured Nazi footage or Allied liberation footage. And everything in color was from when "Night and Fog" was made in 1955. One of the extras on the DVD I watched pointed out that at the time combining old and new footage in the same film was unusual, and combining B&W and color footage in the same film had (almost) never happened before. Since then those techniques have been reused quite a bit (often for either flashbacks or dream sequences) and don't feel so unusual to us any more.

(There's a bit of color footage in the middle of Eisenstein's "Ivan the Terrible - part II", which is mostly B&W. And Godard's "Alphaville" contains something similar to mixing B&W with color, which is a few B&W clips printed in negative/reversed B&W.)