Can someone on traditional Medicare be covered by spouse's FSA?

Hello --

 

If a retired person is covered by traditional Medicare can they also be covered by a spouse's FSA account (through spouse's employer) for expenses that Medicare does not cover?  An example being dental costs, since traditional Medicare does not cover cleanings, fillings, etc.  I know there are restrictions with Medicare and HSA plans, but it appears that FSAs are treated differently.  Thanks.