Still trying to get a working idea of how models, textures and animations operate, so now I have another conundrum.
I imported a custom Nexus model with custom textures, then I saw that the birth and death animations had their own models, so I exported, tweaked and imported them back in to use the same texture as the first custom model.
Going great, except for the part where when I build the Nexus, there's the generic warp-in animation, then it just suddenly appears, bypassing the birth animation completely. The death animation works, though, strangely enough.
I checked and the birth animation has been imported properly, it works in the previewer.
There is a "Construction" actor that seems to be related, but I'm still working on how it actually does its thing. It triggers the animations when a "Build" ability is used. I'll get back to you as I learn more.