Based on the results of numerous internet searches I can't find any (post-SQL Server 2000) reason to not use mount points.
The main reason is someone had a bad experience with them (or, conversely, no experience with them) and has completely ridden them off... forever. This is otherwise known as personal preference.
Now, there are some reasons that you couldn't use them. The number one reason I can think of is that a 3rd party driver or application/tool (think filter driver, disk replication, etc.) does not support it. A quick example of this is a block level disk replication tool that did not support anything other than NTFS, with only specific cluster sizes and couldn't go above 2 TB for any specific volume.
Is anyone aware of Windows OS limitations regarding this topic?
No. you can make many, many mount points. In fact, you'll generally have an issue with your device interfaces before you hit any appreciable limit inside of Windows Server (Assuming you're not using a version of Windows Server that is over 17 years old...).
•I've been hearing the claim "the OS doesn't recognize mount points" a lot lately. (Untrue, based on my research into the versions of Windows Server we use).
If the OS didn't recognize mount points, then how would it even let you use a mount point? That just makes no sense.
If the OS doesn't recognize mount points, why would it track them and query their metadata? Also, please note that a mount point is a construct of the filesystem which an OS may or may not support. Not all filesystems you come upon may support mount points, however the most common filesystem in Windows Server is NTFS which in fact does support mount points and it has for a while.
Just to bring this untrue item home even further; Windows Clustering has something called Cluster Shared Volumes (CSVs) which actually use mount points for the volumes... that's a native item using technology. I have to say, whomever told you this needs to be educated in the issue.
Is there any evidence- or experience-based reason NOT to use mount points with SQL Server?
Yes, there is always that one server running Windows NT 4... don't use it there. You may also want to make sure you're running a supported version of Windows Server and staying current with updates.
However, as I described above, there may be 3rd party items that are not supported or do not work properly with them. I'd say drop that provider and find a new one.
It's my understanding that mount points are incredibly useful for segregating workloads.
Mount points are just incredibly useful. There are many ways to use them, the most common is to get around the drive letter limitations (as in, there are only so many) of Windows. The next most common use is to have smaller manageable sized drives (think LUNs, virtual disk[VMDK, VHDX]) to help get away from insanely large and rarely manageable monolith volumes (it's really becomes a problem to manage drives in the 10TB range as a single LUN, virtual disk, etc.) especially on older versions of NTFS where the implementation was less than the possible usage... for example, in older versions of Windows the maximum NTFS size was 2TB.
Workload segregation is another great use. You can definitely see, there are many uses and it depends on your individual use case. There are also improper ways to use it... such as making a blanket statement that everything needs to be a mount point. That's just crazy administrative overhead at that point.