I can answer your questions.
Q. "How safe is it to hack a Wii u?"
A. It is very safe. Just make sure you are running either Wii U v5.5.1 or 5.5.2 There is a very small risk of bricking.
Q. "...maaaaaybe get free games on it?"
A. You can do this altough there are things to consider
PIRACY
You...