With enough training, certainly. The core concepts of SEO are not that difficult. What is challenging, however, is keeping up with all the changes and learning to adapt the strategy.
Many of our clients do have internal teams who do the day-to-day SEO work. Where we come in is to help with the learning curve, to augment their staff by creating content that is already SEO friendly, and by helping them setup and maintain analytics so that they can make smarter decisions about their digital marketing strategy.