[command to execute] 2>nul 1>nul
EXIT 0The 2>nul 1>nul will swallow the stderr and stdout from the command. The EXIT 0 will make sure the build event returns 0.
This post explains how MSBuild decides whether or not a command executed in a build event has failed. If you control the command your executing, you may be able to change how it writes to stderr and stdout and avoid swallowing those streams. If you don't control the command, you'll have to swallow.
This technique may not be helpful if your build event is more complicated. But if your situation matches this simple scenario, the technique works like a champ!