Can a small amount of scandium be added to gold, platinum or palladium to create a wedding ring?
The go-to place for alloy information is ASM International's Alloy Phase Diagram Database (providing your institution has access). 

Scandium-Gold: as noted in the comment by @MaxW, you can get several atomic percent (but less than 10 at.%) Sc in Au. There exist 6 compounds across the diagram which you would want to avoid most likely. 

Scandium-Platinum: likely up to about 10 at.% of Sc in Pt. At least several compounds to avoid.

Scandium-Palladium: also order of 10 at.% of Sc. 5 compounds to avoid.

All the compounds should be avoided because (1) they are higher in scandium content, and (2) they are mostly line compounds and unlikely to be malleable.

So, yes, you can get scandium in to a gold-platinum-palladium mix. Find a good jeweler and they can melt it in for you. Scandium is not all that expensive (at least compared to the cost of getting the jeweler to do a custom alloy).