So in your experience you have observed it?
Praying to the saints and our Blessed Mother is very much a part of my prayer life. If it’s truly an inter faith service it should be accommodating to all faiths.
If it’s truly an “inter-faith service,” you will see not only various types of Christians (Protestants, Catholics, and the occasional Orthodox), but you will also see Jews, Muslims, Hindus, Buddhist, Scientologist, LDS, JWs, the B’hai, Native Americans, Pagans, Wiccans, and many other "religions, and representatives all of these will most likely be invited to pray a prayer out loud that is from their “faith tradition” and NO ONE is allowed to proselytize or denigrate any one’s prayer or their religion.
So your prayer to the saints would be perfectly acceptable.

You could even pray it kneeling or prostrate, and in Latin.
In our city, I play piano for such a service. It is held not with the motive of actually praying, but to express tolerance of and love for others. It is also meant as a learning experience for those who wish to meet people of other faiths and learn about their religion.
I see nothing wrong and much good with participating in such an event. I know very little of religions outside of Christianity and Judaism, and I think it is good to be knowledgeable, at least in a small way, about those who are not Christians. I want everyone to know Jesus Christ and be part of His Church, and that means that I need to know what people believe in other than Jesus.
One group, though, that you will probably not see at true “interfaith” services is Evangelical Protestants. They generally stay away from these events, as they refuse to appear as though they are endorsing the false religions, or the religions that are opposed to Jesus Christ, Messiah.
Does this sound like some of the “traditional Catholic” thinking that I am reading on this thread?
The problem with this is that the Evangelical Protestants appear as intolerant, fanatical, unfriendly, and willfully ignorant. I spent years as an Evangelical Protestant, and I really don’t think that they accomplish much by staying away from “ecumenical events.” Many Evangelical Protestants donate large amounts of money to missionaries who go to the lands where the Hindi, the Buddhist, the Muslims, Pagans, etc. live. But they ignore the non-Christian people who live in their own cities and neighborhoods. That makes no sense.
Why not invest the time in meeting these people, learning about their faith tradition, and being friends with them? It will take years, but the constant and unfailing quiet witness of the Christian may, through the Holy Spirit, gradually win over the non-Christian. What a wonderful thing!–to be the instrument that God uses to lead someone to Jesus and to heaven!