If you want to add support to hide field labels on a field by field basis, simply add the following line of code to your themes (functions.php).

What this code does is adds a Field Label Visibility dropdown under the Appearance tab in your Gravity Form field (see screenshot below).

Gravity Forms

Hiding Sub-Labels

You can hide sub-labels from the dropdown, illustrated below:

If your labels are still viewable, ensure you do not have malformed CSS structure in your Gravity Forms or Template style. Placing the code below, in the bottom of your style.CSS file will rectify the issues.