I do not think you can truly say that Balaam was claiming in all truth, that the God of Israel was the One true God. This chapter does show that Balaam did have knowledge of the God of Israel and did seek Him in time of need. However, we see ultimately, that even though Balaam knew the will of the LORD (which was that the LORD would not curse HIS chosen & blessed people), Balaam still entertained the thought.
The actions which Balaam takes, reminds me of what Matthew 7:21 says, “Not everyone who says to Me, ‘LORD, LORD,’ shall enter the kingdom of heaven, but he who does the will of My Father in heaven.”
I think looking at Matthew 7:21, one can actually see, that truly to claim the God of Israel, the One true God, isn’t through any words you can say, but it really is a heart issue. Though Balaam knew of God and even heard from Him; ultimately He did not listen and do the will of the Father. -JH