No. While you could
theoretically use a 6-layer board, the G-Boy is really designed for a 4-layer board. Besides, you’ll want to use a 4-layer board for most portables anyway. 4-layer boards use a lot less power and produce a
lot less heat. If you were to use a 6-layer board, you may run the risk of it getting too hot, and the RVL-PMS has a thermistor to prevent that by shutting down the Wii, so you may also get intermittent shutdown.
Here are some of the differences between 4- and 6-layer boards.