There is no requirement that an amendment be germane. Several amendments to this bill certainly were not germane, for example one would have extended unemployement benefits.
A amendment can be quickly killed or ruled out of order if it is not germane to the underlying bill. I have seen this happen many times.
It's also the reason Cantwell's unemployment extension amendment went down.
"...when operating under a general unanimous consent agreement in the usual form on a bill or resolution, amendments must be germane. Germaneness of amendments is also required once the Senate has invoked cloture; in addition, any amendments considered under cloture must have been submitted in writing before the Senate's vote on cloture."