There are several factors suggesting that he might be a Christian... and the phrase which he used in "scarecrow" was "god of all", which cannot possibly refer to a polytheist religion or atheism. Therefore, it narrows down the search.

Since his favourite book in high school was the bible, it suggests that he has been under Christian influences. Then there is hyde, who seems to have overwhelming Christian influences in his works, (or one of those branches anyway) and English-Gothic-Wannabe thingies. 

But angels are quite a commodity without ties to solely Christianity (or one of the Abrahamic religions)... particularly when people started building imaginary religions from the concept of one of these existing religions, in manga, for example, which is very ambivalent towards a specific religion. That's beside from the fact that Christianity is a very widespread religion that's not limited to particular cultures. The influence of Christianity, widely speaking, is very plausible because a) he did say his favourite book in High School was the bible, b) Christianity and its subdivisions are practised widely by Westerners, who has influenced Japan alot, c) Christianity is rather popular in Japan.

However, it seems that he does not truly believe in Christianity, despite its seemingly heavy importance. It seems like he would most likely be an agnostic theist, just heavily influenced by Christianity... Logical people who has the ability to think objectively would very likely be either aethist or agnostic, but, he doesn't seem atheist. And of course, Romantics are more likely to be theists, although he seems to bear the looming questions towards God and regarding this subject.

What is also interesting is Hyde's seemingly strong influence (or co-influence, which is likely) on Tetsu's ideas with regards to God. Tetsu himself does not have much material upon which to base his religion and concept of religion upon (that is, for us to know), because his lyrics often convey emotions, thoughts, and other down-to-earth concepts rather than high-flown concepts. It is very likely that Hyde is a major influence in Tetsu's religious viewpoint (for info on Hyde's viewpoint, read Semi Psycho Analysis of Hyde)