Does the plugin import product categories from eBay?

Yes, the Import from eBay to WooCommerce add-on will import not only all products from your eBay store to WooCommerce, it will create all your eBay Store categories in WooCommerce as well.

Will it import subcategories as well? 

The entire category hierarchy from your eBay Store is imported - categories, subcategories and even category sort order will be mirrored in WooCommerce. 

Please note that for this to work, it is vitally important that you don't have any existing categories in WooCommerce already, especially none that have the same names as your eBay store categories.

And it will assign imported categories to products automatically?

When importing products, the importer will assign each created product to its product categories automatically. If your item was assigned to multiple store categories, it will be found in multiple product categories in WooCommerce as well. 

Again, this only works if the product categories were created by the importer itself. You can not create categories manually in WooCommerce and expect the importer to add new products to them. Sorry :-(

Can it also create product categories based on the official eBay categories?

No, the importer can only create WooCommerce products categories based on your eBay Store categories. The primary and secondary eBay category are stored with each product, but only for the purpose of updating (revising) the listing from within WordPress.

See this page for more details.