RESOLUTION

Note: This is case INsensitive, so all these options work: ZA ,za_ , zA_ or Za)
See if this rule works:
If we create the table below:
CREATE TABLE testRules
(
col1 NUMBER,
col2 NUMBER
)
We get this:

Once we add the prefix za_ , rule 7005 should disappear

STATUS
This rule has been added in Toad for Oracle 13.0 as Rule 2141 ("Make sure the given Schema Prefix name exists for all objects.") .The latest version of Toad for Oracle can be downloaded here