When the engineer carries out the annual radio inspection, part of the job is to check the accuracy of the VOR of course.
The tech uses a piece of equipment that generates known radial's and he/she adjusts the course knob until the deviation bar is in the centre. It's a JAR-145 requirement that they then record the deviation error even if its zero.
JAR-145 states that if you carry out an aircraft task that has a measurable result, then the result must be recorded. Even if they are not a JAR-145 organisation they should still record the result if they are worth their salt. Why not ask for the test results? Maybe one VOR is accurate and the other one needs a 'tweak'. Maybe they are both only 2.5° apart and this is acceptable to you. Either way you will know what you're dealing with.
Regards
The Doc