lt could be possible to get a shiny Pokemon from the Entree Forest.
l'm sure it isn't pre-determined, since you can restart again to get that Pokemon with a different nature, so it should be possible, but alas, it is still a 1/8120 chance to get a shiny Pokemon.
And it's also even more annoying to soft reset in the Entree Forest because you have to turn on your C-Gear first, in order to warp there, than try again.
lt's not a very effective way of trying to get a shiny Pokemon, but possible.
Good luck if you're trying it! ~