The information below has been tested with JProfile 5 on Linux 64bit, and assumes that the JProfiler Agent is installed in folder /opt/jprofiler5.
While this post refers to a rather old JProfiler version, I am sure the principles apply also to more recent JProfiler version. 
 
The following environment variables must be set before starting Virgo: 
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/opt/jprofiler5/bin/linux-x64
export JAVA_OPTS="$JAVA_OPTS -Xbootclasspath/a:/opt/jprofiler5/bin/agent.jar -agentpath:/opt/jprofiler5/bin/linux-x64/libjprofilerti.so=port=8849"
If your JProfiler installation is not located in /opt/jprofiler5 change the above paths accordingly.

A convenient method for setting the environment variables consists in creating a setenv.sh file in the Virgo bin folder. If such file exists, it will be invoked by the startup.sh script.
 
Additionally, it is necessary to modify the java6-server.profile file contained in the <VIRGO_HOME>/configuration folder to ensure that the property org.osgi.framework.bootdelegation contains the com.jprofiler package, as in the example below.
Note: do not replace the file content, just add the com.jprofile.*,\ line.
org.osgi.framework.bootdelegation = \
 org.eclipse.virgo.osgi.extensions.*,\
 org.eclipse.virgo.osgi.launcher.*,\
 org.eclipse.virgo.kernel.authentication,\
 com.sun.*,\
 com.jprofiler.*,\
 javax.xml.*,\
 org.apache.xerces.jaxp.*,\
 org.w3c.*,\
 org.xml.*,\
 sun.*
After applying the above changes, start Virgo and connect using the JProfiler GUI.