The site below has some vbscript code using diskpart that returns information concerning the health of a Windows software RAID. I have not tried it--it looks good; buyer beware. You could adapt it for use in Xymon by writing to a file in the bbwin/tmp directory instead of stdout or piping stdout to a file in bbwin/tmp.
http://www.anchor.com.au/hosting/dedicated/monitoring_windows_software_raid
Ray
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