Is it possible to connect merchant acquiring for an individual entrepreneur without opening an account with Uralsib?

Yes, this is possible. You can use Acquiring from Uralsib even if your account is opened with another bank. The reverse situation is also possible: you can accept cashless payments from another bank's acquiring service into a current account with Uralsib. At the same time, please note that in such cases the commission and the time frame for crediting funds may differ from the standard terms.