Well he bowled well in England without batting well, and I can't shake the feeling that the latter came first (as he's clearly never going to prioritise his bowling and rightly so) so I'm not sure whether he's right or not.
TBH, while practicing your bowling might affect your ability to practice batting (apart from the basic energy-level truths, there's only so much time in a day you can practice in), bowling in a game, provided obviously you're not being run into the ground, won't affect your ability to bat, provided you have a decent break. Which Kallis, being a number-four, is hoped to have.
If you've legit reason to think Kallis is right that too much bowling affects his batting, sure, pick five bowlers. But if you believe he's fussing about nothing, tell him that. It's the job of the selector to get the best out of a player, and if that includes trying to bend him out of his own mental blocks, that's what you must do.