I'm not a member of ETS, but I'm at their annual meeting each year (along with several thousand others) because the Evangelical Philosophical Society meets at the same time and place. Many of the EPS members are also ETS member--including Beckwith. In practice ETS leans very heavily to Reformed theology (some members have spoken openly about trying to erradicate the Arminian heretics from their membership), but the doctrinal statement is merely as follows:
"The Bible alone, and the Bible in its entirety, is the Word of God written and is therefore inerrant in the autographs. God is a Trinity, Father, Son, and Holy Spirit, each an uncreated person, one in essence, equal in power and glory."
Beckwith says he intends to remain a member of ETS because he continues to agree with the statement, but wants to spare the society from adverse attention.
I'm not sure what to think about this yet... I'm all for ecumenism and believe Beckwith to be a brother in Christ. There are decided theological differences, though, and it's difficult to know how significant we ought to make these.
Jesus is probably somewhat troubled by his so-far-unanswered prayer in John 17 that we all be one. Denominationalism certainly has its faults (there are more than 33,000 distinct Christian denominations worldwide now); but I guess I'd like to claim that the preservation of important theological traditions is not one of them. None of our denominations has a corner on the truth, and at their best they serve as helpful correctives to each other.