But you have to take care doing this. The source may not like having pin 3 shorted to ground which is what would happen if you tie #1 and #3 or connect #3 to the input RCA jack's shield.
If this is indeed a problem, it should be plainly stated in an owner’s manual. I’ve never seen or even heard of any warnings of this kind, and I used to install pro audio for a living. (Of course, that was a good number of years ago – maybe things have changed since then.

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Keep in mind that lots of gear has 1/4” TRS connections as well as XLRs, and it’s generally accepted practice to use unbalanced TS plugs with them, which accomplishes the same thing as shorting Pins #1 & 3.
Do you know of any manufacturer who recommends not jumping pins #1 & 3? This is something I’d like to look into, for my own edification. Typically the only reason Pin #1 is floated is for noise issues.
Not jumping across Pins #1 & 3 doesn’t necessarily mean you end up with Pin #3 not being shorted to ground. Pin #3 would carry the shield connection from an RCA (i.e. the RCA’s sleeve connection). The shield connection is common with ground in unbalanced equipment. So, the “balanced” component’s Pin #3 ends up shorted to the chassis of the unbalanced component.
Regards,
Wayne