It is usually discouraged, and many manufacturers say not to do it. Gold is a noble metal that does not oxidize. Tin forms a thin oxide layer that is broken when the contacts mate. When tin is paired with gold, small movements from vibration or thermal cycling can wear the tin and build up oxide and debris in the contact, a process called fretting corrosion, which raises contact resistance over time.
Dissimilar metals in the presence of moisture can also corrode galvanically. How serious that is depends on the metals involved, the environment, and the amount of contact movement.
The safest approach is to mate the same plating on both sides, or to use a pair that the manufacturer has specifically qualified together. If you must mix finishes, confirm it with the manufacturer, and test the assembly under vibration and temperature cycling that represent real use.
