I have set the iOS restriction Viewing corporate documents in unmanaged apps to Blocked but I want to allow my users to still use 3rd party keyboards in iOS apps like Outlook, OneDrive, Word, etc.. Is there a setting that will enable this exception?
Yes. If you use app protection policies (MAM), you can configure this.
Intune App Protection - Properties > Data protection > Third party keyboards
If Viewing corporate documents in unmanaged apps being set to Blocked interferes with the keyboard policy, then I would suggest using app protection policies to enforce the document behavior instead of the configuration profile restriction.
Technically this works for Outlook and the other Office apps, but for some of our non Microsoft apps documents can be sent to unmanaged apps (Workday, ServiceNow, ProjectWise). I wish Apple provided a way to enforce these restrictions on certain apps so I can use Intune policies on other apps.