In an InDesign document, what styling will be applied to text that is imported by a Variable Article Link?

If the Variable Article Link is assigned to a Text Frame, the styling of the imported text will be similar to the styling that you would see if you were to use File > Place to import a plain text file into that frame. For example, if the Variable Article Link imports Plain Text, then the document's default Paragraph Style will be applied. If the Variable Article Link imports formatted text, then the formatting of that text file will be retained. 

If the Variable Article Link is assigned to Text (the Variable Article Link is being used as a Text Link inside a text frame), then the styling that has been assigned to that linked text in the document will be applied to the imported text. Additionally, you can assign a Link Rule to apply a Paragraph Style and a Character Style to that Text Link. In that case, the Rule's Styling will be applied after the text has been imported. In other words, the result will be similar to using File > Place to import the text file to replace a selection of text and then applying the selected Paragraph and Character Style to that imported text.

NOTE: The ability of a Link Rule to apply Paragraph and Character styiling has been designed specifically for Text Links. If the Variable Link is instead assigned to a text frame, then the rule will not apply any Paragraph or Character Styling.  

TIP: To set an InDesign document's default Paragraph Style, deselect all content in the document, open the Paragraph Styles panel and select the desired Paragraph Style. Then, you may prefer to close the Paragraph Styles panel (this helps avoid inadvertently setting a different Paragraph Style as the document's default Paragraph Style before merging).

For more information about Variable Article Links, see Tutorial #1a (The Basics) in the DesignMerge Tutorial Manual, available in PDF format in the DesignMerge product folder on your system.