elgo, you don't understand this vulnerability then. This is a privilege escalation bug that requires code to be executed. If you can exploit a different bug to execute code, this bug won't help you in UBNT land, because you will already have the permissions necessary to do anything you want.
Let's put it this another way - UBNT gear likely has this race condition, and is vulnerable. But it doesn't matter, because to actually be in a position to exploit this, you wouldn't have any need to.
If you are in a position to execute something as root, you've already won the game and this exploit will not help you in any way. In your example of a router running multiple daemons, consumer routers and most Linux-based enterprise router appliances commonly do not implement multiuser security. If you can exploit another bug or misconfiguration in a daemon to run code, this exploit will not help you gain additional privileges, because you already have them all.
The vulnerability existing or not is boolean. Actual exploitation and attack surface is not. One must understand the vulnerability and the equipment to make this judgement. The UBNT judgement makes sense in this case - UBNT units may technically have a kernel that is "vulnerable" to this exploit, but in practice, it's completely unhelpful. There is no additional "risk" whatsoever by this bug on UBNT products.
Edit: far less words saying the same thing in the reply before mine.