Which "Visitor ID" are you talking about? and how do you collect the data if you don't use DTM?
notmally you could write the default "Visitor ID" (Experience Cloud Visitor ID) to any of your dimensions (eg. eVar) to make it available for reporting.
a) in DTM/Launch add the value to any prop/eVar, eg. eVar1=D=mid
b) use processing rules to "copy" value to a prop/eVar, eg. "overwrite eVar1 with VisitorID"