Amanda,
Unless you are running totally separate businesses, you should not need a separate unsubscribe page. You can use Domain Aliases to help manage that of course. There are articls on this.
Marketo will merge leads across domains if the lead fills out a form on BOTH sites.
If you need to keep the leads totally separate, then I'd make a Segmentation based on the domain visited or use a hidden field on all forms to do this.
Anonymous leads won't matter here because they'd be separate and hidden, unless you are using RTP.
See these articles
https://community.marketo.com/apex/MarketoDiscussionDetail?id=90650000000PivMAAS
https://community.marketo.com/MarketoResource?id=kA650000000GtnhCA