Yes.
I know JWE2 gave us pretty much all of JWE1's dinosaurs, but that was a very special case. JWE2 was released less than a year after JWE1 was finished and from what we know from the leaks JWE2 came into being because they were cornered on a technical level in JWE1. With the deadline of a new JW movie on its way and Universal calling the shots, JWE2 had to be there faster than they probably wanted so the only way not to loose your entire audience was to give them all the dinos again right from the start.
If Planet Zoo stops now and we get the sequel in, let's say November 2026, there is plenty of time for a new audience to join the game that did not play the first game; and there's enough time to have big enough improvements for Frontier to be able to sell animals we already had in this game. If not, as you pointed out, it's pretty much impossible to go on a multi year DLC plan as we'd just get multiple Arid-like packs.
I'd say that if we get a Planet Coaster 2, we should be preparing ourselves for a Planet Zoo 2 for sure and we're more than likely aren't going to get all animals from the first game. (Which by all means, is not uncommon at all)
From the looks of it the rig started from their flamingo rig, but even if it didn't;
we know enough about Frontier's rigging process that even a completely unique rig is not
that special.