CustomGame.GetLoadCount(List<int> playersConnected);
Syntax
public int GetLoadCount(
    List<int> playersConnected
)

Returns the number of players that are invited but not ingame, caused by using CustomGame.InvitePlayer().

The example below will invite Tracer#1818 to the custom game, and display a welcoming message when she joins.

using System;
using CustomGameOW;

...

static void Main(string[] args)
{
    CustomGame cg = new CustomGame();

    // Send an invite to Tracer#1818, wait for her to join the game, then send an message welcoming her to the game.

    cg.InvitePlayer("Tracer#1818"); // Invite Tracer#1818 to the game

    while(true)
    {
        int ingame = cg.playercount - cg.GetLoadCount(cg.playerslot); // Get number of players ingame rather than slots filled
        if (ingame > 0)
        {
            cg.Chat("Welcome, Tracer, to the game!");
            break;
        }
    }
}

See also:

CustomGame.GetLoadSlots()

CustomGame.InvitePlayer()