Hmm. Good question. As I recall that universe, to the extent that Valdemar has any religion, it's that the Heralds are good and the Companions are mystical-magical good. And there is a special Companion Grove in the center of Companion field and super special Companions sort of appear there without have been born before hand.

So I'm thinking, the Grove is probably holy ground, possibly the field is as well. I'm not sure whether or not simply riding a Companion would count. Hmm.