Hi Andrew,
I suspect you intended to reply to an existing thread instead of creating a new one. I'll try to answer the questions you posed above without the context of the original discussion.
You can determine if a module supports the ISearchable interface by logging in as a host user, selecting Host/Module Definitions, and selecting the edit link for the module in question. The "Searchable" checkbox indicates whether DNN detected that the module in question supports the interface.
The search indexer should be scheduled with the following parameters:
Type: DotNetNuke.Services.Search.SearchEngineScheduler, DOTNETNUKE
Frequency: Every 30 minutes / 60 minute retry (by default)
Enabled: Yes (duh? :)
Retain history: 60
Run on event: None
Catch up: Unchecked
Object Dependencies: SearchEngine
Hope this helps!
Brandon