As far as I know, the specification is not available yet, so the only way to tell is to try it.
I installed VS 2013 RC, so I thought I could check using this union:
type Expression =
| Add of Left:Expression * Right:Expression
| Constant of number:int
As expected, it does generate named properties, which are nicely useable from C#:

In fact, it also uses the name in parameters of the construction functions:

If you're using them for C# interoperability, then you'll probably want to write the union member names in PascalCase
, because the compiler does not automatically capitalize the name of the property if you use lowercase name (but interestingly, it does use a lowercase name for the parameters).