You can "interview" with any agency you want, while you are working at a different brokerage. You are not working "for" anyone, since you are an independent contractor... but be aware... if your current agency catches wind that you're looking to leave... they may decide to force your hand.
I don't know the details of Keller William's model... but I doubt they pay a salary. Call your local KW office (or an agent at the office, if you're friendly with one) and ask them. Don't jump ship until you have a lifeboat to land in.