/usr/local/apache/htdocs/thecenterforhealthenhancement.com/wp/wp-content/uploads is the correct full directory path to /uploads. And I can drag things in and out of it freely via ftp; has 777 permissions, so isn't that basically wide open?
Just tried define('PCLZIP_TEMPORARY_DIR', ABSPATH.'wp-content/updraft'); as an alternate – same outcome, same error.
Is this for sure a permissions issue? Just poked around further up the chain... see that I have no permission to directly access /usr or /local or /apache in the chain. Can see contents of /htdocs, and noticed that /thecenterforhealthenhancement.com folder within has more restrictive read/write permissions (750), then folders within it.