I don't cast baits, but it seems to me, if casting under pressure produces micro bubbles, that would be a good thing.
First, there won't be any large bubble voids at or near the surface of the bait, which could cause cosmetic problems or weak spots.
Second, if the micro bubbles still rise in the material before it sets, and you pour with the belly down/back up, the bubbles will be higher in the bait, and that will make them more stable, because the back will be more buoyant.
But that's just looking at it from an outsider's perspective.
People who actually pour resin baits will know a heck of a lot more than I.