I believe that developers choose the language as per the project requirement based on the following factors taken into consideration.
# Language is good enough for client/server side applications. I believe GO is good at writing server side applications.
# How much learning curve involved if someone knows Java/C/C++?
# What kind of online support GO is having?
# Are there enough tools/libraries available for GO as we compare to Java?
# There must be good debugging support with language.
# If some one is having existing java/c++ apps. How newly written GO app would interact with existing c++/Java written apps?
Yes, Go is good for writing server side applications.
I think Go is easier to learn than C, C++, or Java. However, Go does require you to think differently about object-orientation (so is probably easier for C programmers than C++ or Java). Also, since Go does memory management you don't have to worry about returning local objects.
There are far fewer tools/libraries for Go than for Java---after all Java's had a 15+ year start! You can see what's in the standard library here Go Packages and what's available from third parties here Go Dashboard.
You can interact with C++ or Java applications the same as you would between any applications that are written in different languages: for example, read/write files or use network connections, etc.