Here is the solution I ended up using to capture and email the thread dumps. It doesnt redirect STDOUT of the process, it just grabs the pertinent info from catalina.out.
#!/bin/bash
CATOUT=/opt/tomcat/logs/catalina.out
DUMPSTART=$(grep -n dump|tail -n1|cut -d':' -f1)
DUMPEND=$(wc -l $CATOUT|cut -d' ' -f1)
kill -3 $(pidof java)
sed -n "${DUMPSTART},${DUMPEND)p" $CATOUT |mail -s "Java thead dump" myemail@foo.com