Are CEREC Crowns a Good Option for Back Teeth That Are Not Seen?

Yes, no problem. However if money is an issue, a less costly gold, porcelain fused to metal or Empress crown is fine too. 

If prepared in the appropriate manner, CEREC crowns are a wonderful option for posterior ("back") teeth.  In my experience, these crowns are just as successful, if not more successful, as laboratory-fabricated crowns (whether procelain-fused-to-gold, full gold, or porcelain-to-ziconia or some other material).  Every individual is unique, and some individuals do not have adequate tooth structure or may generate too much force for a CEREC fabricated crown to be successful. With materials like e.max (lithium disilicate) available, the strength of CEREC fabricated restorations exceeds that of many laboratory-fabricated materials.

The accuracy and precision of CEREC is unsurpassed compared to traditional impression techniques used for laboratory-fabricated restorations,  and the appropriate materials used under the appropriate conditions with CEREC can produce a long-lasting natural-looking restoration for a posterior tooth.

Cerec technology is wonderful for inlays/onlays and allows to save time and money for both a practitioner and the patient. However, the research shows plenty of evidence about failures of Cerec crowns (all-ceramic) crowns used for posterior teeth. The Cerec crown never will be able to adapt the same amount of occlusal load as standard PFM crown which is lab-made, it doesn`t have the same strength, glaze, etc. In a long term prognosis patients usually face a lot of problems like chips, cracks and will require the re-make of the Cerec crown. As a Prosthodontist I won`t recommend the use of Cerec crown for posterior teeth and will navigate my patients towards more stable, long-term predictable results with lab-made crowns.