First of all, I'll say outright that I believe that none of us have all of theology exactly right. If all the followers of God in the world combined the truths that we know, we still wouldn't have the right idea entirely.

That being said, I believe that if you seek God, he can be found. If you call out to him, he will draw you to himself. Theologically speaking, I do not believe it is appropriate to pray to Mary or the saints, because they are dead people, and are no longer concerned with this world. At all. However, if someone is praying to Mary to intercede to God, of course God is going to know, and he will hear that prayer. He's not going to say "Bam! I smite you for not praying to me in my proper name!" or something like that. But an honest heart seeking God will find him. If the channel is totally inappropriate, hopefully God will reveal the right channel to that person.

Then there is the issue of idolatry. Praying to an image of Jesus probably is not idolatry, because the person is still praying to Jesus. If the object of their prayer is actually the image itself, then THAT is idolatry. Mary is a gray area. I think it's just as silly as praying to an idol, because she can't hear prayers (not being God and all that), but the idea is kind of praying THROUGH Mary to reach God. It's unnecessary, for sure, but idolatry? Not necessarily.

Just some thoughts,
Hikaru