Yes, there is some risk because the 1099R and 5498 will not match up in IRS computers when the rollover is reported. There has been former PLRs allowing a decedent’s distribution to be rolled over to an inherited IRA (in one case with the estate as beneficiary), and the surviving spouse is then able to secure the balance by assigning the IRA as executor to herself, and finally to assume ownership of it).
It is surprising the custodian is willing to bypass all these steps as well as assuming these PLRs can be applied to this client. I doubt that many custodians would allow this. The mismatch mentioned above could be avoided by the custodian allowing the rollover back to the inherited IRA so that the 1099R and 5498 would conform. If they conform, the IRS will assume the rollover was actually completed by the decedent and the account numbers would also match up as required by Notice 2020-51.