Resolution:
Assuming that BW 5.1.2 installation on Solaris 2.8 performed by root:

If you are starting "Domain Hawk Agent"  using a user account other than 'root', it will look for vpd.properties.* in user's HOME directory instead of 'root'  directory which is the actual location of these files.
  
There will be additional issues involved, for example, Administrator may not recognize the installed application and you cannot deploy any application.

This is currently by design. If you want to use a different user to start the process you should create a softlink to the installed vpd files in the user home directory for the specific user.