Employee security clearance is a major issue for organisations, and even more so in positions of sensitivity such as admin, root or super-user roles. My usual thumb, is to assume that these roles can do much more damage than a normal user so heavily protect your organisation from them. Traits may be the wrong word though - as many traits of highly skilled professionals are the same as highly skilled criminals.
In some countries this is easier than others, but basic security clearances include credit and criminal checks (if an individual is heavily in debt they become more amenable to persuasion from criminal elements, and a criminal history should rule out individuals for sensitive roles, especially if it was a crime associated with IT fraud.) Known associates should also be researched.
For highly sensitive roles, regular rechecks may be required. And an awareness of your employees behaviour could be a value add! Salaries should also be reviewed - underpaid roles are a straightforward target for bribery and corruption.
This doesn't really change if the individuals has unique skills, as underlying the roles should be an infrastructure which prevents misuse, for example restricting administrative rights to only those required should be a given. For most platforms, root or Administrator access is not required, so where relevant a Power User or lower should be used, and root should be restricted to emergency occasions - where it requires input from two individuals:
an example:
Database admins often demand full superuser rights, but this is almost never needed. There are many types of admin role which can be assigned as appropriate, and root can be a break-glass role which requires retrieval of a password from a safe, or from two individuals each holding half.
To summarise - yes, IT gurus are essential but dangerous; protect yourself from them with technical and procedural controls, research their background and use their skills to add value.
