I sit in way too many policy and compliance meetings than is healthy for any one person. I've never seen a non-fraternization rules that does not include consultants or vendors. The folks writing these things know what they are doing - their job is to protect the organization from legal fallout. They're not going to say "well it's not quite as bad banging a vendor as a co-worker, so let's leave it out". There is absolutely no incentive to not be as broad as possible.Sorry if this has been covered, but most corporations' code of conduct governs contractors as well as employees.
Not that this matters anymore, but your company's policy is lenient. My company has a ban on relationships between senior/subordinate and any intra-company relationship is supposed to be disclosed.
Don't like the rule? Quit. Otherwise, there is a universe of people that probably do not represent 99.9999999999% of the people that would be covered in such a clause that you can bang freely.