Crawler and Federated Search

Hi

I would like to use the Crawler to index the content but instead of it going into its own index, I would like to use the “Index Time Merging” type for Federated Search. Is it possible for the Crawler to push documents into a pre-existing index?

What are the pros and cons of this approach? I will have multiple crawlers and APIs pushing into the one index.

Thanks,
Sam