I haven't used that page-excerpt plugin before, so I don't know how it works. I would try it and improve WP Carousel to make them compatible, but I'm a bit busy this month, so I think I will not be able to do that until december.
In any case, if Page Excerpt uses WordPress's custom fields to store the excerpt of the pages, it will be really easy to use them as description.
WP Carousel tries to load the value of custom field WP_CAROUSEL_CAROUSEL_TEXT and use it as description for any content, but as in most of the cases that custom field is empty, WP Carousel also loads the excerpt of the post.
WP_CAROUSEL_CAROUSEL_TEXT is a constant, defined in wp-carousel.php near line 71. Just change "wp_carousel_carousel_text", the value of that constant with the name of the custom field that Page Excerpt uses and then WP Carousel will use the excerpt of the pages.
But this will only work if in fact Page Excerpt plugin uses custom field, and I'm not sure about that as I haven't used that plugin before.
Thanks for using WP Carousel, I'll try to implement this feature ASAP.