Yes, using switch_to_blog()
you can load another WordPress site, get what you want, then revert back to your current site and carry forward any retrieved data.
// the different site ID in your WordPress Network
$otherSite = 3;
// the post excerpt you're after in the different site
$otherSitesPost = 42;
switch_to_blog( $othersite );
$otherSitesPostExcerpt = get_post($otherSitesPost)->post_excerpt;
restore_current_blog();
echo "Site #{$otherSite} post #{$otherSitesPost} excerpt: {$otherSitesPostExcerpt}";