Server A produces signed messages on request. You can tell server A what type of RSA padding to use in the signature (either RSASSA-PKCS1v1_5 or RSASSA-PSS). Either way, the message will be signed using the same private key. The signed message is a JSON object where you can supply some of the fields, but the server supplies the others.
Server B accepts these signed messages and verifies the signature using server A's public key. You have the ability to select which padding scheme that server B should use to perform the verification (again, either RSASSA-PKCS1v1_5 or RSASSA-PSS).
Is it possible to abuse the ability to switch between padding schemes in order to tamper with the message? Is it possible to cause server B to misread fields in the JSON object that were supposed to be supplied by server A?