No, and in fact they appear to show the exact opposite.
For example, in this YouTube clip you can see Caitlin using her right hand to wield a hammer, followed by Killer Frost using her right hand to use her freeze power. Similar clips show Reverb clearly using his right hand as his dominant hand.
It's possible that Black Siren was just lying: she clearly suspected what Cisco and Caitlin were up to, so she was bluffing. If they looked scared or caught off-guard by her claim, she would know they were fakes. When Caitlin even says "Reverb was left handed" when Black Siren knows full well he's not, that gives them away.
More likely, it's just a continuity error because no one thought about it while they were filming the earlier scenes.