The Kobolt Oracle?

[The Aboleth]

What I say is that the assumption that The Oracle didn't know that Roy would bypass the Memory Charm, is based only in Roy's inmediate conjecture after the event.

No, it's not; another person already pointed out that The Oracle is regularly caught unawares at the most personally inconvenient of times:

Indeed - this is even illustrated in his first appearance: I can peer into the murky depths of the future and yet I always seem to get interrupted during bath time.

So clearly his future-seeing powers aren't always "on," meaning that he's probably not omniscient. So that is at least one point of evidence in favor of the "It is plausible The Oracle didn't look ahead to see if the Menory Charm was bypassed" theory.

But there is no reason for the Oracle to restraint from banishing Roy (and getting rid of him ASAP, since he dislikes dealing with him) because of the bypassing, as the information Roy would keep doesn't hurts the Oracle and helps making Roy more distrustful of Belkar, who the Oracle aslo hates.

Roy doesn't need any help distrusting Belkar--he had plenty of other reasons both before and after this incident to distrust Belkar. Plus, Roy has no reason to think The Oracle would help him, and the Oracle has outright stated the only reason he deals with people at all is because he pays them. Heck, the Oracle puts Belkar's death "on the record" precisely because he thinks Roy wouldn't believe him otherwise!

Again, for someone accusing others of making assumptions, you're sure making plenty yourself.

Fact:
A) By banishing Roy, The Oracle let him bypass the Memory Charm.

No, that's definitely not a fact.