Only customers on this forum can answer that question individually. I would say that the Oracle Spatial staff may not as it is more a sales question. But even if they knew, they probably are not allowed to say (a marketing issue).
But I can say that, as a consultant, I have clients who run Locator on both Enterprise Edition and Standard Edition. And lots of people downloading my solution samples from my website who must be running Locator on SE.
In effect, Locator was released for SE customers, so one would expect that there are thousands out there running that combination.
For what reason are you asking the question?
There are indeed may success stories for Locator.
Appendix B Oracle Locator of the manual deals with the differences .... here is the headline info
Oracle Locator (also referred to as Locator) is a feature of Oracle Database 11g Standard Edition. Locator provides core features and services available in Oracle Spatial. It provides significant capabilities typically required to support Internet and wireless service-based applications and partner-based GIS solutions. Locator is not designed to be a solution for geographic information system (GIS) applications requiring complex spatial data management. If you need capabilities such as linear referencing, advanced spatial functions, or Spatial Web services, use Oracle Spatial instead of Locator.