I assume you are meaning VHF not UHF. Marine VHF is between 150 mhz and 162 mhz. Australian CB UHF is between 476 mhz and 477 mhz. Receive wise you may not see much of a difference as radio reception on varying length antennas is not detrimental to your radio,, HOWEVER transmitting into a non resonant antenna is hugely detrimental. If you transmit into a UHF antenna with a VHF radio on 25 watts unless there is some sort of protection fold back unit in the radio your finals are damaged and likely not working. You would not notice it because your receive function will still work. You will be able to transmit,, well it will look like you are but only milliwatts will come out. You don't need the dealer's antenna but you do need a marine VHF not Air VHF and not Amateur (Ham) VHF no matter if they all use the same standard screw in base.
Bear