It is not correct to say that traditional unions aren't interested in allying with the FOP or the police in general.  As a union lawyer working with "traditional unions", I am familiar with ongoing efforts on the part of local unionis  to maintain good relationships with local police and their unions, and this is, at least sometimes, extremely important in picketing situations.  Houston is not a union town, to say the least, and my hunch is those unity efforts between police and the rest of organized labor are not to be found.

Incidentally, under long-standing federal labor law, the National Labor Relations Board will not certify a proposed collective bargaining unit that includes both guards and non-guards.  There is an inherent tension between private security personnel and non-security personnel, just as there is an inherent tension between workers serving in a police capacity and the general public.  

Let's not condemn all of those who serve in law enforcement; they are working people too.