Yes, this text does not directly address the issue of praying to Mary and the saints. But the idea of appealing to anyone but God was obviously not present in the mind of the Psalmist. If we (as did the person who wrote this Psalm) can place this much trust in God, then there is no purpose or need in petitioning saints and angels. We should entrust ourselves to God alone.
Furthermore, we who are on earth cannot know (apart from some supernatural revelation or manifestation) with certainty which of these so-called saints truly went to heaven. Only God knows the hearts of man. Thus, it is highly possible that Roman Catholics are petitioning powerless people who are now spending eternity in fiery torment. It is best that we reject mystical ideas and stick with Scripture as our final court of authority.