That got me thinking a bit and did a bit of research on XML in SQL databases. A bit easier if the XML is actually stored in an XML datatype vs the nvarchar this field is stored in, but luckily a "CAST" seems to work.
Try this, I think it actually works!! Might need some tweaking, esp. changing <YOUR RULE NAME> to a specific rule, or removing that part of the query if you want a count of all violated rules...
SELECT CAST(PCR.XmlResults AS XML).query('count(//Ps)'), PCR.RuleName, N.Caption, N.IP_Address FROM NCM_PolicyCacheResults PCR
JOIN NCM_NodeProperties NP ON (NP.NodeID = PCR.NodeID)
JOIN Nodes N ON (N.NodeID = NP.CoreNodeID)
WHERE (PCR.IsViolation = 1) AND (PCR.RuleName LIKE '%<YOUR RULE NAME>%')
GROUP BY N.NodeID, PCR.RuleName, N.Caption, N.IP_Address, PCR.IsViolation, PCR.XmlResults
ORDER BY N.Caption, PCR.RuleName
Kinda neat actually...
