[ball]

You have got function OnVehicleUpdate, but you never call it. You have to set timer

Код:

public OnFilterScriptInit()
{
	return SetTimer("OnVehicleUpdate", 1000, 1);
}

forward OnVehicleUpdate();
public OnVehicleUpdate()
{
	new Float:health;

	for(new playerid; playerid != MAX_PLAYERS; playerid++)
	{
		if(!IsPlayerConnected(playerid) || !IsPlayerInAnyVehicle(playerid)) continue;

		GetVehicleHealth(GetPlayerVehicleID(playerid), health);
		SetProgressBarValue(Vhealthbar[playerid], health);
		UpdateProgressBar(Vhealthbar[playerid], playerid);
	}
}

Not tested, should work. Also i recommend show progress bar in callback OnPlayerStateChange, not in OnPlayerEnterVehicle - this callback is called when a player begins to enter a vehicle.