We need the home page and a footer module to display different content based on the subdomain the visitor is coming from. Can the URL condition include the subdomain (sub1.example.com, sub2.example.com, etc.)?
If yes, can the URL condition include a wildcard, i.e. sub2.example.com/* ?
Yes, the URL condition includes the full domain.
You don't need wildcards in this case, as it just looks for whatever you tell it to inside the full URL.
So to make it show only on URLs containing 'sub2.example.com', just put that in the condition.