Just got my Keylab 49, made some tweaks in Reason, and it's now working the way you describe. It works perfectly, but you need to change your preferences in Reason, not the Midi Control Center - I'm using Reason 8.3, but it will work with any version.
Open your Reason Preferences and make sure KeyLab49 is set as the Master Keyboard
Then click on the Sync Tab - you'll see there are 4 Busses A-D
Set Bus A to - KeyLab 49 then close your Preference window
Switch to the Reason Rack and find the Hardware Interface - it's usually at the top of the rack. This is where you set your Audio I/O, switch to the Big Meter, or make Advanced MIDI settings. Which is exactly what we want to do.
Click on Advanced MIDI - in the fold down window, make sure Bus A is selected and displays KeyLab49
Click on MIDI Channel 10 and you'll see a menu of all the devices in your Rack - send MIDI Channel 10 to the "In" of the Kong Device you want to control with the Pads.
Bang your Pads - hear that?
You're done - now go make some music.
P.S. If you want to go crazy you can open up the Arturia MIDI Control Center and split your Pads into 2 sets of 8 pads. That way you could control an OctoRex with pads 1-9, and your Kong with pads 9-16.
Open the Arturia MCC and set pads 1-9 to transmit on MIDI Channel 11
Sync your KeyLab to the new settings
Go back to the Reason Advanced MIDI settings in your Rack.
Set MIDI Channel 11 to the "In" of the OctoRex you want to control.
See what we did there - now go make some more music!
Hope that Helps.