Ah!Both are correct. Usually a company has a number of policies - saying "it is not company policy" means that what is being described isn't included in any of them. If you use "the", it would suggest that you are talking about a specific policy, and that what is being described is contrary to that policy.
For example, a company might not give donations to charity, but not have any specific policy about donations. It would be correct to say that it is not company policy to give donations to charity. Another company might have a policy to donate only to medical research charities. It would be correct to say that it is not the company policy to give donations to a pet shelter.
If we say the company's policy, the article refers to 'company', because if we can say turn the phrase into an 'of-phrase', then the article refers to the noun in possessive case. But in "the company policy", the article, on the contrary, refers to the head noun (policy). That means that possessive noun and attributive nouns act differently?As an alternative to the frequent "it is not company policy to", I would say "it is not the company's policy to", which is mostly what you get if you search on Google.
You can also say "it is not the policy of the company", which naturally becomes "the company's policy", not "the company policy".
However, I hesitate to use correct since it is difficult to find out which alternative is least used. I would say it's more a question of style.