Can a Protestant or non-denominational Christian can fully participate in the sacraments and life of the United Catholic Church?
Absolutely. Denominations are a creation of man, not Christ. There is only one Body of Christ, and baptism into the Christian faith, regardless of the denomination (or lack thereof), is the point of incorporation of an individual into His Body. We do not put man-made rules above what Christ himself created. All baptized Christians are welcome to participate fully in the United Catholic Church.