Is it possible for these models to be merged into a single model and use bodygroups to switch between helmets and other such things?
It’s pretty much possible no matter who does it as long as they know what they’re doing. The only problem is finding someone willing to put in the effort.
Source has a 32 texture limit on a model, putting all those models into one would probably overshoot that limit.
That’s probably the only other problem you’ll hit, but that depends on what you’re going for. I didn’t actually look at the newest pack, though; I had no idea it had so much in it now. Assuming you only wanted to actually use about a dozen of these since a lot of the variants are random, just for some different styles, you should be fine, but it may require a lot of merging and uv editing depending on how it’s all handled.
In other words, if you only wanted to keep a few specific variations, you can probably have dozen head variants, a couple body variants, and some different skin variants for the bodies (whereas the heads automatically use these materials). I’m bad at explaining things.