Good question. I went back and reviewed some old movie footage of 163's flying during WWII and at first glance it appears that they had extended flaps for landing. But on more careful viewing, the flaps are not on the trailing edge of the wing. They are flat panels on the lower surface only, and are about 60% of the way back from the leading edge. So they are in fact spoilers, not flaps. They would be used to steepen the glide path to assure an accurate landing spot, just like any modern glider.

The spoilers on the 163 are no doubt positioned such that they create little or no pitching moment, while at the same time creating needed drag. Note also that the 163 isn't really a delta wing. It's a swept wing tailless aircraft. So the actual position of the spoilers is quite near the CG compared to the elevons.

Link to movie below. You can see the extended spoilers on landing at about 2:50 and at 4:12 into the movie. And then a pretty clear shot of the lower surface of the wing at 4:42.

Dick

https://www.youtube.com/watch?v=kMScNZFg0k4