I'm not using a Mac nor UEM and therefore can't help with a detailed and tested solution. But what about searching in WWW for
Safari command line and try the tips you find.
The first page in results list of google.com is a forum page with subject
Launching Safari from the command-line. According to last post
open /Applications/Safari.app '%f' might work.
The second page in results list of google.com is
Invoking OS X apps from the command line. According to this page
open -a /Applications/Safari.app '%f' would be the right command.
Is there an
Output tab on user tool configuration dialog of UEM? Yes, is there an option like
Show Console/Terminal? Yes, then uncheck this option for this tool.
UltraEdit for Windows has also an
Options tab where the user can select the
Program Type. Browsers are on Windows OS Windows applications and therefore
Windows program must be selected instead of default
DOS program. Has the user tool configuration dialog of UEM also an
Options tab where the
Program Type can be set?