shouldn't this be "do you ahve some password?" as in a password that may or may not exist?
It doesnt sound like you were asking someone if the person has a password or not. Its more likely to be related to someone asking if it's necessary a "password, sign, ticket, voucher" to enter somewhere or you wait in the line
so "senha" can be anything required to pass a checkpoint?
When the verb TER (To have) is conjugated in the 3rd person, it can mean the same thing as the verb HAVER (There be). It's impersonal.
It accepts "do you have any password". It is also an option.
Would this be used more often than "Ha uma senha"?
In everyday life, yes
It ought to accept "passcode" in as well, I reported that to have it changed
It is also acceptable. "Passcode" is also translated as "Código de acesso".
Can this mean "Do you have...."
A person would probably use "você tem...", even when you have a context.