It was, for at least some versions (V2 and later?), if the intermediate site(s) allowed execution of the uucp command. 25 years on the brain is fuzzy on the details ...
You could certainly add uux and uux to the list of legal remote commands, but I confess that my memory is also dim about whether uucp file a!b!c would be translated automatically. It has indeed been a while... Yup. The real work was done by uucico (using an x.21 type protocol implemented by Greg Chesson of EGREG fame if I remember correctly). UUCP and friends where front-ends for it and has been reimplemnted as the honeydanber version. Then there were the AT&T Basic Network Utilities version, Taylor uucp, the EUUG version etc. of these. jaap