as far as i know the frame under a blazer and the frame under an s10 PU is the same thing. i also believe that the 2wd axle from both the blazer and the PU are the same size. this is the same for the 4x4 rear axle in both the blazer and PU which is about 3-4 inches wider than the 2 wheel drive axle.
the ZR2 rear axle is wider still than the blazer or s10 4x4 axle. i just dont know by how much. i have heard that its about 2 inches wider. which would make it about 6 inches or so wider than a 2wd axle. El Beautor is running a ZR2 rear and i have asked him about it because i want the 8.5 inch rear end. he said that with the ZR2 rear it pushed his tires out even further than it did with the regular 4x4 axle. his tires currently stick out past the fenders in the back. if i were to do it with stock rims, mine would probably be damn close to even with the fronts. and mine is 4x4 but NOT ZR2. so if i got the ZR2, it would solve everything that i am looking to do in that respect.

so to answer your question condensed like you have 3 different axles
2wd either PU or Blazer <-- skinny, rims have big offset (they have a big dish in them)

4x4 either PU or Blazer <-- wider, rims have less offset. (they appear flatter from the outside)

and ZR2 rear. <-- widest of the 3. i wouldnt put 2wd rims on it....4x4 rims only. my.02

 

There is no difference between the s10 pickup axle and the Blazer axle other than the Blazers spring perches have the rubber bump stop cup and the S10's do not. Other than that they are identical depending on drive type just like you said (2wd, 4wd, ZR2).

I'm fairly certain that the ZR2 axle is just over 3" wider than the 4x4 axle. My ZR2 axle is about a 1/2" wider than my stock 4x4 axle was with 1.25" spacers.

Here is a perfectly to scale example of the 3 axle lengths:

 

thanks El B. i didnt think about the bump stop cup.
and i really like the absolutely perfect, to scale, axle drawings.