No! And you know, I didn't even consider the squishiness of the plastic as a risk for lack of porousness, either!
I have an extra Snuzzle here, I was debating giving her some gradient tips!
I did dye one of the super-hard 25th anniversary ponies, and she took dye like a champ! So in her case, the hard plastic wasn't a deterrent; just a deterrent to me trying to get her silly head off in one piece!
If I ever get around to it, I'll update you!