I don't know if that is the case with Ubiquiti but some products in their line sure looks like it.
Looking at the number of employees working at Ubiquiti versus their revenue, also suggests that (most?) of their products are not designed in-house. That's just speculation of course.
Well the Edge line, and this is me guessing, is likely third party hardware that they buy (that's pretty easy) and they basically use an open source OS barely modified. They were half public about that when they started, so it kinda made sense with that line. No idea if they continued that with Unifi and others.
Well, they started with RF-based products so they have that expertise in-house.
It would make sense that their wifi products are developed by themselves and manufactured by OEMs while the rest are ODM products.
That's the quickest way to expand the product range. Otherwise you need a ton of employees. From the info online they're only about 1000 employees worldwide.