As an Employer, I take a very dim view to my employees 'freelancing' or doing any other work outside of the paid employment spectrum. I have invested time, money, skill and training in them and gave them opportunity. If they want to Freelance then they can hand their notice in immediatley and become a competitor, I don't have an issue with that. If they are caught doing another work apart from company business during work hours it is a standard breach of Employment contract and is a dismissable offence.
I dislike freelancers with a vengence, ( unless they are genuine self employed freelancers who pay tax etc.) They undermine the business, offer cheap rates and take the food out of bona fide business's mouths.
Any employee found doing paid work outside of my company as second revenue stream or competitive area would not have a long term future or be part of any plans going forward. I kind of think that would be across the board for most Employers whatever business they are in Design, Accountants, Bricklayers etc.