Ola Hallengren IntegrityCheck Excludes TempDB
Answer based on a comment left by Randi Vertongen:

Ola mentioned a long time ago (+5 years) on SQL Server Central that this is by default:


  This is by design. DatabaseIntegrityCheck is not doing checkdb on tempdb.


and a way around it by adding it explicitly.


  In the latest version you can do like this:

EXECUTE dbo.DatabaseIntegrityCheck
      @Databases = 'SYSTEM_DATABASES,tempdb',
      @CheckCommands = 'CHECKDB'



He goes on to say:


  When I developed the scripts I was looking at how Microsoft was doing in the Maintenance Plans. They are not doing checkdb for tempdb, so I did also not do that. Some time ago I added support for checking of tempdb, but not as the default. You need to specify tempdb explicitly.


Not entirely sure if this is still the case.