Translation:She discovered that he was unusually stupid.
Yes, definitely, though it's usually a lot more common to just use the past tense. There's no real reason for it, as far as I'm aware. German, for instance, also allows for both but heavily favours the present.
My father speaks German natively, and Swedish on a native level, well enough that almost nobody would think him anything but Swedish. This construction is one of very few that might still betray him as a non-native.
That said, if the "he" in this sentence was stupid but then somehow increased his intelligence, obviously you would need to stick to the past tense.