I'm not under the impression that crows will be cut like they were in REmake 2 because they're hard to implement so much as nothing's added by having them be there (very rare, showing up in only one hallway in the original RE2, go down in a single bullet yet are also small flying targets where auto-aim isn't part of the default controls). Spiders getting cut would likely boil down to clashing with the look/tone they're going for once again (keeping the giant gator in REmake 2 aside) rather than logistics issues.
The Gator wasn't supposed to come back if I recall correctly, but they added him back late in developement for some reason.