Since Verity determines relevance largely based on the number of occurrences of the criteria, one way to "prioritise" results would be to artificially append the SKU multiple times to the "body" when indexing the collection.
You could do this either in your original SQL query, or you could use ColdFusion to massage the resultset to pad it with the SKUs before passing it to Verity. Here's an example of the latter option:
<!--- Get the product data--->
<cfquery name="qProducts" datasource="blog">
SELECT
ID
,SKU
,title
,description
FROM
products
</cfquery>
<!--- Massage the data to prioritise the SKU by creating a new query from the original --->
<cfset qProductsForIndex = QueryNew( "ID,title,body","Integer,VarChar,VarChar" )>
<cfloop query="qProducts">
<cfset QueryAddRow( qProductsForIndex )>
<cfset QuerySetCell( qProductsForIndex,"ID",qProducts.ID )>
<cfset QuerySetCell( qProductsForIndex,"title",qProducts.title )>
<!--- Add the SKU 5 times, separated by a semi-colon --->
<cfset QuerySetCell( qProductsForIndex,"body",qProducts.description & ";" & RepeatString( qProducts.SKU & ";",5 ) )>
</cfloop>
<!--- Pass the massaged query to Verity --->
<cfindex action="REFRESH"
collection="products"
type="CUSTOM"
query="qProductsForIndex"
key="ID"
title="title"
body="body">
Note the semi-colon separating the the extra SKUs, this ensures Verity will match them as separate occurrences.
I've used 5 as an example number, but you might start with just 2 and tune it upwards until you see the results you want.