Yes, you can have Crucible running this way without the need to integrate with any SCM, which means you can have a Crucible license only (not needing a FishEye license). The ingration with SCMs allows you to easily add the content from your repositories to your reviews, but if you like you can have Crucible not indexing any repositories and, instead, adding content to reviews as attachments, as described in this document.
You can read more about how Crucible is licensed at https://www.atlassian.com/licensing/crucible.
Since you didn't provide many details about how you intend to perform your reviews, please let me know if there's anything else that needs to be clarified.
Hi All! We’re excited to share the launch of an announcement banner that lets Jira site administrators communicate directly to their users across their Jira Cloud instance. ...
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