The type of Christian churches that would use manipulative techniques to proselytize Catholics would never get involved in ecumenism to begin with.
The Christian churches that get involved with ecumenical activities are the mainline churches (older denominations; e.g., Lutheran, Reformed, Presbyterian, Methodist, etc.). These churches are very liberal socially and theologically. They wouldn’t use manipulative techniques because they believe everyone is going to heaven (except Republicans and rich CEOs who oppress their employees).
The Christian churches that are likely to use manipulative techniques are the fundamentalist churches, and they would never become involved in ecumenical activities because they are usually separatists who avoid people who aren’t part of their churches.
The Evangelical Protestant denominations will get involved in ecumenical activities that have a stated purpose that is in agreement with their theology. E.g., many Evangelical Protestant denoms and churches but not all) will get involved with pro-life activities or with all-city prayer meetings. Most Evangelical Protestant churches and denominations do not get involved with the general ecumenical councils and movements because they don’t want to work with liberal churches who preach acceptance of abortion, homosexuality, etc.
I personally don’t think that Evangelical Protestant denominations and churches use manipulative techniques. I think they have really really GOOD music–but that isn’t manipulation. Catholics could have good music, too, if they’d stop fighting about music and just do it.
Also, Evangelical Protestants also have really really good preachers who give interesting and timely sermons–but that isn’t manipulation. Catholic parishes could have really good preachers, too (and some do!).
And Evangelical Protestants offer really really GREAT fellowship opportunities and they are generally very friendly churches–but this isn’t manipulation. Catholics could have really good fellowship opportunities and be friendly churches, too (and some are).
As for the altar call that still happens in many Evangelical Protestant worship services–I don’t consider that manipulation, because Catholics have an “altar call”, too, and it’s pretty compelling–Jesus in the Blessed Sacrament calls people to come home to the Catholic Church and and receive Him. It’s the main reason I became Catholic–I wanted to receive Jesus, Truly Present in Body, Blood, Soul, and Divinity!
I guess what I’m saying here is–no, I don’t think ecumenical activities are manipulative. I think that some Catholics who are weak in their faith and who have lukewarm Catholic parishes may be attracted to churches that offer good music, preaching, and fellowship, but to me, these churches aren’t being manipulative. They’re just doing what God wants all churches, including the Catholic church, to do–preach the Gospel in word and deed.