It does not work in the stripping way. It is simply like concatenation.
Dynamically add a new extent. The datastore can span over up to 32 extents with the size of each extent of more than 2TB, yet appear as a single volume. The spanned VMFS datastore can use any or all of its extents at any time. It does not need to fill up a particular extent before using the next one.
Saying above it does not do a stripping or the existing data is not distributed or load balanced among the added DISK/LUN