HIPAA requires employees to be trained based on their job role. Even if you employee is temporary employee. Based on the job role of the person, you will ask them to take necessary training. If you want them to take the basic training, you can ask them to do the Certified HIPAA Privacy Associate (CHPA) training http://hipaatraining.net/hipaa-certification/certified-hipaa-privacy-associate-chpa.htm
which includes HIPAA security overview. If you want them to have comprehensive HIPAA security training then you want them to go through the Certified HIPAA Security Expert (CHSE) http://hipaatraining.net/hipaa-certification/certified-hipaa-Security-Expert-chse.htm
All consultants or companies providing temp staff are the business associate of covered entity. All BA have to comply with the HIPAA regulation. If you have temporary employee, they are still part of your organization and your organization will be responsible if there is HIPAA violation caused due to their action. The key is that the person has to be trained based on their job role.
If you are covered entity, download this questionnaire of HIPAA compliance status of the business associates. This helps you to ensure that BA meets the HIPAA standards. http://www.compliancehome.com/whitepapers/HIPAA/abstract11982.html
Feel free to ask if you have any other questions.