Use the OEMDuplicatorString in sysprep. Then you can use a custom inventory like this:
<?xml version="1.0" encoding="windows-1252"?>
<InventoryClasses>
<InventoryClass name="AeX CI Image Info" manufacturer='Altiris' description='Imaging Information' platform='Win32' version='1.0' mifClass='ALTIRIS|AEX_IMAGEINFO|1.0'>
<xml xmlns:s="uuid:BDC6E3F0-6DA3-11d1-A2A3-00AA00C14882" xmlns:dt="uuid:C2F41010-65B3-11d1-A29F-00AA00C14882" xmlns:rs="urn:schemas-microsoft-com:rowset" xmlns:z="#RowsetSchema">
<s:Schema id="RowsetSchema">
<s:ElementType name="row" content="eltOnly" rs:updatable="true">
<s:AttributeType name="c0" rs:name="CloneTag" rs:number="1" rs:nullable="true" mifAttrId="1">
<s:datatype dt:type="string" dt:maxLength="255"/>
</s:AttributeType>
<s:AttributeType name="c1" rs:name="CmdLine" rs:number="2" rs:nullable="true" mifAttrId="2">
<s:datatype dt:type="string" dt:maxLength="255"/>
</s:AttributeType>
<s:AttributeType name="c2" rs:name="OEMDuplicatorString" rs:number="3" rs:nullable="true" mifAttrId="3">
<s:datatype dt:type="string" dt:maxLength="255"/>
</s:AttributeType>
<s:AttributeType name="c3" rs:name="OsLoaderPath" rs:number="4" rs:nullable="true" mifAttrId="4">
<s:datatype dt:type="string" dt:maxLength="255"/>
</s:AttributeType>
<s:AttributeType name="c4" rs:name="SetupType" rs:number="5" rs:nullable="true" mifAttrId="5">
<s:datatype dt:type="string" dt:maxLength="255"/>
</s:AttributeType>
<s:AttributeType name="c5" rs:name="SystemPartition" rs:number="6" rs:nullable="true" mifAttrId="6">
<s:datatype dt:type="string" dt:maxLength="255"/>
</s:AttributeType>
</s:ElementType>
</s:Schema>
<rs:data>
<%set Key="HKEY_LOCAL_MACHINE\System\Setup"%>
<z:row
c0="<%writexml "reg:%Key%\CloneTag"%>"
c1="<%writexml "reg:%Key%\CmdLine"%>"
c2="<%writexml "reg:%Key%\OEMDuplicatorString"%>"
c3="<%writexml "reg:%Key%\OsLoaderPath"%>"
c4="<%writexml "reg:%Key%\SetupType"%>"
c5="<%writexml "reg:%Key%\SystemPartition"%>"
/>
</rs:data>
</xml>
</InventoryClass>
</InventoryClasses>
Your report would be something as simple as:
SELECT ii.[OEMDuplicatorString], count(*) AS 'Total #'
FROM Inv_AeX_CI_Image_Info ii
GROUP BY ii.[OEMDuplicatorString]
ORDER BY count(*) DESC