H4 dependents can travel to USA, while transferring H1B

Right now, I’m moving my H1b to another employee(Normal processing). I have received H1B receipt number.

H4 dependents having a valid visa with an old employee, can they travel to the USA?

Yes they can travel as far as thr visa is valid. Fyi, Visa is not tied to a specific employer even if the sponsoring employer name is mentioned on the visa.
Just provide the H4 with copy of your current I-797 and the receipt notice for the transfer so in case the CBP will ask at the POE, they can present the documents. Also include copy of last three pay stubs from current employer and the offer letter from the new employer.