Found the answer to my own question. Either Symfony's documentation is a bit wrong or UVdesk application isn't using the normal methods per Symfony's documentation.
I was attempting to use Symfony's instructions here (https://symfony.com/doc/current/bundles/override.html) but it did not work. I was trying to override the login template with a file in 'templates/bundles/UVDeskSupportCenter/Knowledgebase/login.html.twig'. This did not work. I was able to find this semi-related issue in GitHub (https://github.com/FriendsOfSymfony/FOSOAuthServerBundle/issues/557) that got me on the right track.
Using "bin/console debug:twig" I was able to find the correct path which is "templates/bundles/UVDeskSupportCenterBundle"/Knowledgebase/login.html.twig". You need to add that 'Bundle' onto the end of the end of the bundle name as it exists here (https://github.com/uvdesk/support-center-bundle/blob/master/Controller/Customer.php#L102).