When you say "compete," do you mean that you're aiming for advanced titles and high scores, or that you'd just like to be active in the sport with your dog for fun?
If your goal is to go all Seriously Serious about competition, then I wouldn't start with a puppy of totally unknown background.
On the other hand, if you're just in it to have fun and see how far you can go, and you like the puppy and won't be totally devastated if you end up with a loving companion rather than a sport superstar, go for it.
ARCHEX TDCH Pongu the Insane, CD-C, RN, RL1X4, RL2X3, RL3X (GSD mix, b. Apr 2010)
Crookytail the Tigerwuff, RL1, NTD (Akita mix, b. Jan 2011)