A file that would is --exclude'd should not trigger a non zero RC if we can't read the file. For example:

/tmp $ mkdir demo
/tmp $ mkfifo demo/bad
/tmp $ touch demo/good
/tmp $ aws s3 sync demo/ s3://bucket/demo/ --exclude '*' --dryrun
warning: Skipping file /private/tmp/demo/bad. File is character special device, block special device, FIFO, or socket.
Completed 0 part(s) with ... file(s) remaining
/tmp $ echo $?
2

Given that /tmp/demo/bad was never going to be transferred in the first place (because it's been excluded via --exclude '*', it seems odd that this will trigger a non zero RC. I'd expect the RC to be 0 here.