How can I receive a success output signal from command block on a fill clock?

Solution 1:

• /execute @p[rm=6] ~ ~ ~ /say The command worked
• /execute @p[r=5] ~ ~ ~ /say The command did not work

(both after the /spreadplayers command). The only problem with that is that it will still act as if the command didn't work if a player gets positioned inside the 5 Blocks radius.

EDIT: It is now completely possible with the CommandStat Data Tag:

/blockdataCommand Block Coordinates{CommandStats:{SuccessCountName:"Fake Player Name / Entity / whatever you're gonna use",SuccessCountObjective:"Scoreboard Objective Name"}}

Basically, you can make the SuccessCount output to a scoreboard. See the video below for more info!

EDIT 2: Maybe I should mention that you can then do some sort of execute on the entity if it has a score of at least 1. Also, you should set the score back to 0 at the end of every tick (/cycle of the clock).