The PHPVibe Youtube importer functionality relies on the Youtube API (2.0, soon to be 3.0).
The Youtube API has limitations, it limits how much data can you grab from it in the number of requests sent to the Youtube servers.
The most important limitation is the number of videos returned for a query, which varies, and will not be more than 500 results in practice (even if they say up to 1000).
So if you expect to have all the videos from Youtube (for a search), tough luck!
The only way you can bypass a little is to set a cron(or more) to grab daily fresh data, in time you will gather all the fresh videos for your interest (Youtube category/channel/search/daily highlights, etc).
In PHPVibe when Youtube limits you (temporarily) you will notice the following:
– On the importer : No results are returned.
– On the share by link: The video details come up blank (title, description, etc).
For more on the Youtube API please visit Google Developers.