Can I add a blog URL to my main top Magento navigation?

Yes, and there is a special setting for that in System > Configuration > Blog Pro > Top Menu Integration:

Magento Blog Pro by Amasty

1) Display: Select "Yes"if you want to display the blog link in the top menu.

2) Label: Specify the label of the link.

3) Position: Define the sequence of the link among other links in your top navigation.

See more details on Blog Pro page
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