ANY ship crossing the veil. ANY. Quarian or not. For 300 years.
Excuse me please while I call bull**** on this.
Any ship going beyond the veil for three hundred years did not return. First, take a look at the posibilities that leaves us.
1) The Geth attack anyone and everyone.
2) The Geth attack ships that act in a hostile fashion once the Geth encounter them.
3) The Geth don't attack anything, and it's something else in the Veil that disables and/or destroys ships.
Now, let's consider some simple
facts as they are presented in Mass Effect.
1) The Geth haven't been seen outside the Veil in 300 years. This, coupled with the fact that no ship that goes beyond the veil ever returns, could be reasonably extrapolated that Geth haven't been seen in 300 years. (reference: Kaiden in the first mission, several other characters)
2) The
only time we
ever see Geth acting aggressively is when they are under the command of the Reapers, up to and including their instance of self-defense against the Quarians.
3) There is only a small portion of the Geth that is acting under the command of the Reapers. It's not an unreasonable inference to say that Geth that do not follow the Reapers are still non-hostile to organic life. (reference: Legion and his loyalty quest)
So, with that collection of data in hand, we have a set of evidence that Geth do not act aggressively toward organic life under the vast majority of circumstances, up to and including vast enslavement to organic life, but will act in self-defense while attacked. Further, the exposure of the difference in Geth consensus regarding whether to follow the Reapers or not shows that most Geth do not support the destruction of advanced organic life.
Therefore, it is a much more reasonable conclusion that the ships lost in the Perseus Veil are lost either to their own aggressive action toward the Geth, or by some other threat that may lurk there.
Furthermore, the
only instances of synthetic life attacking organic life attacking organic life without provocation and not under the direct control of the Reapers were...
****. I'm drawing a blank. Oh, wait, that's because it
doesn't happen. Now, that's a problem, because the entire ending cutscene hinges on the fact that synthetic life tries to destroy organic life, and that the reapers try to stop that. By trying to destroy organic life. As synthetics.
That's the problem with the ending, Trash. It's bad because it's inconsistent both with the universe, and the themes in the universe up until that exact moment.