Is it acceptable for a Catholic to venerate saints that were canonized by Eastern Orthodox churches? Saints like Xenia of Petersburg, Seraphim Sarov, and Maria of Skobtsova lived very holy Christian lives, and pose as a model for all Christians.
While it is certainly possible for Catholics to admire the Christian witness of those recognized by Eastern Orthodox churches to be saints, and while it is also possible for Catholics to learn from the lives and writings of apparently holy people of other Christian faith traditions, I cannot recommend giving such people the honor Catholics accord to those who have been recognized to be saints by the Catholic Church. Canonization by the pope is an infallible statement by the Church that a particular person definitely is in heaven and therefore worthy to be given public honor by Catholics. Although the salvation of non-Catholics is hoped for, we have no such absolute knowledge that those “canonized” by non-Catholic churches are indeed in heaven.