What is the opinion of employers about *BSD?
I presume you are talking about employers in the computer and IT industry; for employers and jobs such as catching fish, being a medical doctor, or playing the oboe in the symphony orchestra, BSD is not relevant (nor is Windows or Linux, for that matter).
So let me answer the question in two separate parts.
One: Do many employers use BSD? No. Most commercial computers run Linux, followed by Windows, followed by commercial Unixes (HP-UX, AIX, Solaris, ...), and the market share of BSD is tiny (roughly 1%). If someone has BSD-specific skills, that is not relevant. There is a very small set of BSD-specific employers (iXsystems for example), and there is a small set of companies that use BSD (such as Netflix, Juniper and NetApp), but they typically hire generalists, not people who only know BSD.
Two: Employers like to hire people with skills. The most important skill that employers look for is the ability to learn and grow. If you want to be a programmer, sys admin, software engineer, product manager, SRE, and so on, you have to demonstrate general computer skills. Ideally, on a wide variety of platforms. So learning to use computers on a BSD machine helps demonstrate the breadth of skills, and the ability and willingness to learn new ones. That's the same as programming languages: In a modern software engineer job, C++, Java, and a good scripting language are pretty much mandatory, but there it helps to demonstrate mastery of Haskell, SQL, Go, assembly, and so on.
There is reason for to learn use *BSD to find job?
For computer-related jobs: Yes, see above. Although honestly, many of the same skills can be learned on Linux too. And for specific sys admin skills, since most employers use Linux, and few use BSD, learning Linux has advantages.
Graphic design is a different set of skills, in which the computer part is not terribly relevant. Same with playing the oboe in a symphony orchestra: the employer will want to know how you sound on the oboe, not whether you know how to mount a ZFS file system. But again, a breadth of skills is important: a good oboe player needs to understand music theory, know how to conduct, a little composition doesn't hurt either. The need to play music in a variety of styles, from baroque to Queen. And being able to double on trombone or viola wouldn't hurt either.
If there is not reason for to learn use *BSD to find job, why use *BSD?
Because it is useful. For example, I have a set of computing problems that I need to solve in my house: firewall and router for the internal network, store files and documents, make the printers accessible, and so on. For that I need a computer, a.k.a. server. In my opinion, BSD is best at doing that (whether OpenBSD or FreeBSD is a fascinating discussion), but that's just my personal opinion. Other people could use Linux or Windows for the same purpose, depending on their taste and their skills.
