You complained about SOAP/MGE not working... when you didn't enable plugins.
You complained about SOAP not working... on a map for which there are no spawns.
You complained about a sourcemod command not working....which works just fine when I use it on the server you're on.
I just went on 3 random serveme.tf servers and ran "rcon sm_cvar tf_dropped_weapon_lifetime 0" without issues.
rcon sm_cvar tf_dropped_weapon_lifetime 0
autokick is disabled for Arie - serveme.tf
[SM] Changed cvar "tf_dropped_weapon_lifetime" to "0".
L 11/02/2015 - 00:41:45: [basecommands.smx] "Console<0><Console><Console>" changed cvar (cvar "tf_dropped_weapon_lifetime") (value "0")
[SM] ADMIN: Changed cvar "tf_dropped_weapon_lifetime" to "0".