Like @StoneMagnet said, they should be located there. Similarly though, I have none in there to verify that.
I'm not entirely sure, but I think panic logs end with a .panic extension. At least that's what I seem to remember. If I'm correct, you should be able to write an EA to capture the number of them within a certain timeframe (just so you aren't worrying about panics that happened weeks ago for example)
#!/bin/sh
PanicLogCount=$(find /Library/Logs/DiagnosticReports -Btime -7 -name *.panic | awk 'END{print NR}')
echo "<result>$PanicLogCount</result>"
The above would give you a count of panic logs found that were created within the last 7 days. Anything older won't get included. It will typically show "0" as the result. If you save the EA as an integer type, you can create a Smart Group that would show anything with more than 0 results so you can keep track of Macs that have any kind of panic logs within the last week.
You can change the -7 to something lower or higher of course.
You might need to verify that the panic logs actually get created with the .panic extension on them. I can't verify that, so I'm just going on memory. I may be wrong about that though.