[RyDeR`]

Use a variable; I recommend to use PVars.

In /boatDM and other DM commands

Код:

SetPVarInt(playerid, "InDM", true);

In /leavedm (dont use /leaveboatdm, otherwise you have alot of commands)

Код:

SetPVarInt(playerid, "InDM", false);

At the top of OnPlayerCommandText

Код:

if(GetPVarInt(playerid, "InDM")) return SendClientMessage(playerid, 0xFFFFFFFF, "You cannot use commands while you're in a deathmatch zone. Use /leavedm to exit!");

I recommend to use one variable so you have to use only one command (/leavedm) and also one check under OnPlayerCommandText.