The help text says the the syntax is <x of orgin> <z or origin> <distance between players> <distance from origin> . . . The affect (or at least the message sent) seems to suggest that the syntax is really <distance from origin> <x of origin> <y of origin> <distance between players> . . .

example: I typed /spreadplayers 0 0 400 1000 true @a
I expected this to spread all players (teams respected) at most 1000 blocks from the point 0,0 with 400 blocks between each team.
The result text says that command spread the teams 0.5 blocks from the point 0,400, with 1000 blocks between each team