A check is a Shtar, exactly like it was in the time of the gemorah, when someone wrote “Harei Ani Chayav” in a Shtar and it was valid.
The Halachic status of a bank account in general is interesting. L’cheora the money in the account is on loan to the bank (since it can use the funds as they wish, within reason & the law). Adding money to a loan doesn’t require a kinyan per say.
The money is owed to the poel for his/her work. By agreeing to transfer that “loan” over to the bank by all of the parties involved, and giving the use of the money to the bank, the bank is now responsible for the loan to the poel, and the employer is no longer responsible for the loan.
In short, I would think (but in no way am I a posek) the kinyan is not required, and the shibud transfers from the employer to tha bank (possibly due to a Rav Nosson type arrangement).