Planting moles in foreign organizations is the explicit purpose and core competency of foreign intelligence agencies. It's only inside the US where that activity is (supposed to be) forbidden.
You should assume that the US intelligence community is already doing this to foreign tech corporations and has been forever.
That's exactly my point. It was supposed to be forbidden domestically and that added trust to US-made technologies. However, now that we've learned that US companies are completely fair game, the level of access the government has to domestic companies via moles, NSLs and other acts of espionage, we should assume that domestic companies are far more compromised than foreign companies. This assumption is not only reasonable but the responsible assumption to hold if you are a foreigner.
You should assume that the US intelligence community is already doing this to foreign tech corporations and has been forever.