We see why the dog gets infected, it's right there in the EEV when the fafehugger reveals itself. In my book, that makes it a heck of a lot more likely than the oxen, who's living conditions we know nothing about.
Also it's worth pointing out that even in the assembly cut version, the dog still exists - Murphy calls out for Spike before he gets killed.
There's any number of reasons for the dog to be there - it stowed away on a transport, etc. When it's trivially easy to explain why a dog would be present, that's the opposite of "illogical". Like, there is obvious logic to explain the presence of the dog, independent of whether you believe it to be likely or not.
I'd buy a dog being present at the colony before I'd buy Ripley making it out of the EEV when it crashes.
Also the EEV's crashed state in the assembly cut introduces a fun continuity error that isn't present in the theatrical cut - in the TC, the EEV crashes with the starboard side submerged, while in the AC it's the port side submerged. Given where the EEV opens (the starboard side) and the order of the cryotubes from port to starboard (Hicks, Bishop, Ripley, Newt), it makes sense in the TC that Newt drowned since her tube was the most likely to be underwater. In the AC, with the port-side crash, the only way for Newt's tube to be underwater is if all the other tubes are, too. What with Ripley's having a gaping hole in the glass, shed have drowned along with Newt unless she was awake and alert before/during the crash and got herself free. Given how the two prior movies showed that cryotube occupants are groggy for a good while after waking up, that's probably not likely. Not to mention that Kane was real groggy after he woke up from getting facehugged- so Ripley would be fighting off the effects of the cryosleep *and* the facehugging to get out before drowning. Possible? Maybe. Likely? I kinda doubt it.