If you're frustrated trying to figure out how to use the Jetpack Comments for with one of these Rocket themes after selecting "Use WordPress Comments" and it doesn't show, the solution is fairly simple (but not good if you upgrade the theme and need to do it all over again):
(1) Use FTP or other means to access html/layouts/commentstempl_standard.php.
(2) (a) Near the bottom of the file there's a section of code that includes the comment form, between the
<form> </form> tags. Delete the entire block and replace it with
<?php comment_form(); ?>, which is the code for inserting the standard WP form. (b) Comment out the form heading "Leave a Reply" located between H2 tags just above the code you've commented out.
(3) Activate the Jetpack Comments from the Jetpack dashboard if you haven't done so already.