Doesn't really matter, you're really attaching to studs, not the wall panels. The wall panels are there for decoration, and as long as you use the appropriate hardware and attach them to the studs, the studs will carry the load (assuming they were done correctly behind that wall.

Yes, like Steve J said, make sure your lag bolts grab a stud. However, you didn't mention installing power and signal cables, as I'm assuming you want a clean look over the fireplace. Installing an AC outlet and running your signal cables (COAX, HDMI, Category cables, etc.) can be a bit challenging only because you can't patch paneling (if power/signal is not already present). If it's a simple 1/4" paneling it may come of easily and allow you to run wires - if it's 1/2" or 3/4" bead-board (I can't tell from the photo) it will be more difficult. Another option, rather than concealing wires in unsightly wire-molding, is to remove the paneling altogether, run your wires and create a facade different from the rest of the room - something as simple as painted drywall, or you can get creative with other types of materials such as stone, brick, etc. It's a bit more work, but it makes for a very nice look. Good luck!