Yes, it's very possible. You do not want to be in the same room with evil entities, even if you're not the one consorting with them. Demons don't care who invites them. Once they show up, whoever is there is open game.
This is why an exorcist recently warned the public of Oklahoma City not to attend a black mass that is scheduled to take place in the Oklahoma City Civic Center on September 21, and especially not to do so out of curiosity, thinking they're somehow safe because they're not really "praying" to Satan. Everyone in that room is in grave danger when Satan arrives, regardless of their intention.
Even though Reiki masters don't deliberately invoke Satan as is done in a black mass, they do invoke a "spirit guide" which is a demonic entity. They like to think it's a kind of guardian angel but this is not possible. First of all, because the spirit guide helps them to become attuned to a universal life force which is a kind of god, or creating spirit, in the New Age. This is not the God of Abraham, but a false god identified in the document, Jesus Christ, the Bearer of the Water of Life as "the New Age god." Second, the Almighty would not permit His angels to participate in any practice associated with the worship of false gods.
Just because they don't believe this "spirit guide" is a demon doesn't mean it isn't! Nor does this denial protect them in any way from the effects of this entity.
It's also important to note that practitioners pray to this entity before each session. ThisReiki Master recommends that her colleagues "Ask for assistance, protection and guidance from your Spirit Healing Team (which may include your guides, angels, Ascended Masters, Usui sensei, Reiki Masters or Divine Source, etc.)
This practitioner offers a prayer that reads, in part: " Lord, my God, I offer you my humble presence, To be the comforter and the reliever, As I recognize myself as part of your unlimited source of goodness and Healing; I consciously request the right to be reconnected with the Universal Life Force."
If you've had a Reiki massage, the first thing to do is renounce any spirits that were present in the room during your massage. Say, "In the name of Jesus Christ, and by His power and His authority, and through the powerful intercession of the blessed Virgin Mary, I renounce any spirit that was present in the room during my Reiki massage. In the name of the Father, the Son and the Holy Spirit." This prayer should be repeated three times, once for each member of the Trinity.
You should also confess having participated in Reiki massage to a priest.
After this, be at peace.