Nixon is the typical example of somebody pardon'd without an indictment. Like it would be wise to imply it could happen because it has!
There are a other trivial examples. Confederate solders weren't indicted [1]. The Vietnam draft dodging pardons didn't even name people [2] [3].
Why they would do it? I mean to nullify the 5th amendment right. Maybe you want to prosecute a crime boss so you give somebody a pardon (or immunity) so they can't/don't plead the 5th and have to testify against them.
You're arguing, with no evidence, for a claim with counterfactual precedent. (And look up preemptive pardons. Not been done. But you're lacking imagination if you can't see the utility of a pardon absent indictment or even accusation.)