Is it covering the vent, as if there was no vent there (imagine your index finger on the vent, and that's the same visual that I'm referring to regarding the tom hardware mount covering the vent)? If so, it would change the response of the drum (and slightly - you may not be able to hear it) as well as the tone.
I would liken it to a bass drum with a solid resonant head versus a bass drum with a ported resonant head, as it relates to the different levels of repsonse.
I know that Yamaha and Pearl does different things with the position and number of vents, which to their claim, brings more bottom end and response/resonance to each drum.