I believe you can invite the user to join your Jira instance, but don't provision them with access to the Jira application itself. You should then be able to configure the Service Desk project so that anyone with an existing account in Jira can create a ticket. This should also allow them to use single sign on via their G Suite account.
There's an important differentiation between having a Jira account and a Jira license. You can technically have an unlimited amount of Jira accounts in your user database, but you don't have to provision them with a license that would count towards your license count. Application access and license provisioning is granted based on whatever user group gets a license to Jira (usually something like jira-software-users if you haven't changed the default configuration). As long as you don't add the user to whatever group(s) get a Jira license, you should be fine. :)
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.