Is it safe to create a Bitcoin account for another party? Is this a scam?
This is unsafe and definitely a scam.

One common way it's done is as follows.  Using your login and password, the guy will secretly retrieve the recovery phrase for the wallet.  He will then let you change the password.  Then, he will make up some story to convince you to acquire some Bitcoins and put them in the wallet (or maybe he'll just wait until you decide to do so of your own accord).  You will think this is safe because he doesn't know the new password.  However, using the recovery phrase, he will be able to take all the coins from the wallet, even without the password.

If he really just wanted access to a Blockchain wallet, there would be nothing to stop him from just making one for himself.