No, that's a different module. See the "2.3 branch" sticky in the DOM forum.

OK, I've got the 2.3 versions of both event_calendar and dataobject_manager installed. I ran http://localhost/silverstripe/index.php/db/build?flush=1 and http://localhost/silverstripe/index.php/dev/build?flush=1. When I try to add a date to a new CalendarEvent, I get the following JavaScript errors:

Error: $(this).parents("div.datepicker:first").metadata is not a function
Source File: http://localhost/silverstripe/dataobject_manager/code/date_picker_field/datepicker_init.js
Line: 5

Error: setting a property that has only a getter

Error: $("a[rel=clear-btn]").live is not a function
Source File: http://localhost/silverstripe/dataobject_manager/code/date_picker_field/datepicker_init.js
Line: 9

Is there some incompatible jquery file cached somewhere that I need to flush?

Since a module I really want to try/use (Workflow) doesn't work with SS 2.3.7, I'm going to abandon it and try the 2.4 version. Looks like a lot of the Event Calendar stuff is different/updated/fixed for that version, so don't waste time looking at this issue.

Just so you know to rebuild the database you only need the following:

[siteaddress]/dev/build?flush=1

dev/build has replaced db/build, so you only need to do dev/build

Also, you shouldn't have the index.php in your address. So if you site address is http://localhost/silverstripe/ then your database rebuild call should be:

http://localhost/silverstripe/dev/build?flush=1

I got same error with @logiczero until now :(