I think that, without having to read further on in the series than the priest's tale at the beginning of the first book, Dan Simmons is offering up some pretty interesting commentary against the catholic church. After all, you're asking if the cruciform, as described in the priest's tale, is a "symbolic criticism against the catholic church", and so here are a couple of points that, in my perspective, answer your question with a definitive "YES".
- The cruciform is worn like a cross necklace, but it is horrifically described from Paul Dure's perspective as a parasitic organism that is impossible to part with once it merges with your flesh -- Simmons' representation of the crucifix as a parasite is fairly obvious critique.
- The cruciform, once merged with your flesh, can offer eternal life. This would appear to be the ultimate reward to a follower of the church, but as you previously observed, the cruciform continuously eats away its bearers intellect, free will, and identity each time he/she dies. I suppose that this could be interpreted in varying ways. It's possible that one could read into this and make an argument that, once an individual has been "saved" and achieved "everlasting life", there is no further need for a personal identity, as said individual has overcome their human and individual flaws, and is gradually evolving towards a communal state of perfection (I often thought of the H.G. Wells' Eloi with Simmons' description of the Bakura tribe). Adversely, the opposing argument would be that no reward is great enough to justify the cost of one's identity and intellect, and that the ultimate reward is actually a trap to bend the masses to its will. Simmons' appears to fall in the latter camp and is actually satirizing the church's ultimate reward -- human's are gifted free will by the creator, only to have it stolen away once they accept the church and bear its symbol.