Employers (and therefore recruiters) may see shared intellectual property (IP) as an issue. If you apply for a salaried position as an information worker (software developer, artist, composer, etc), many companies will require you sign over all IP created while employed to that company. This will definitely affect your freelancing work.
Employers (and therefore recruiters) may also see it as a potential conflict of interest. Freelancing for a potential competitor is a big risk. Similarly, accidentally or deliberately using knowledge gained in your salaried work in your freelancing work is also a risk. Employers may also feel freelancing is a distraction from your day job.
That said, most will not care if the positions are unrelated (e.g. you are employed as a software developer but freelancing as an artist) or valuable to the company and you can manage your time well. Freelancing can give you different and better experience, particularly soft skills (e.g. dealing with customers, self promotion and managing expenses) and exposure to different markets, products and techniques.
It really comes down to how you sell yourself. If you are confident and can demonstrate that your freelancing experience makes you a better employee, recruiters will see it as a plus.