Yep, it is possible. When JATS Parser plugin is turned on, Old Gregg theme starts to use the JATSParser lib from this plugin, which has newer version. Some changes are associated with links parsing. Particularly, this part of a template should be rewritten: https://github.com/Vitaliy-1/oldGregg/blob/master/templates/frontend/parser/text.tpl#L23-L36
I am planning to update Old Gregg theme so it stay inline with update JATSParser library in September-October. It should move away from using Smarty templates as injecting full article’s HTML is much more easier approach.