The HOTAS Warthog is indeed "plug and play", but as you have noticed the trim hat is mapped to viewpoint by default. You can remap this in the DCS control menu.
First, delete all of the "view" assignments.
Navigate to the A-10C Sim "View" page, scroll down to the view functions, click on each view assignment to highlight, then click the "Clear" button to remove it.
Next, add your trim assignments.
Navigate to the A-10C Sim "HOTAS" page, scroll down to the trim functions, double-click an assignment to bring up the assignment dialog, actuate the appropriate key/button (in the case of the pictured example, trim hat left) and the assignment will appear in the "Key/Button" field. Click "OK", Repeat as necessary.