Opencast includes ORGANIZER only if there is a Presenter (DC Creator) in the metadata. So the lack of an ORGANIZER: field is not a problem to any existing CAs because Opencast allows scheduling events without a presenter name.
Second, Opencast's use of the ORGANIZER field in the ical feed is not standards-compliant. Specifically,
Conformance: This property MUST be specified in an iCalendar object
that specifies a group scheduled calendar entity. This property MUST
be specified in an iCalendar object that specifies the publication of
a calendar user's busy time. This property MUST NOT be specified in
an iCalendar object that specifies only a time zone definition or
that defines calendar entities that are not group scheduled entities,
but are entities only on a single user's calendar.
Description: The property is specified within the "VEVENT", "VTODO",
"VJOURNAL calendar components to specify the organizer of a group
scheduled calendar entity. The property is specified within the
"VFREEBUSY" calendar component to specify the calendar user
requesting the free or busy time. When publishing a "VFREEBUSY"
calendar component, the property is used to specify the calendar that
the published busy time came from.
From a standards point of view, it makes no sense to identify the presenter as the ical ORGANIZER because the presenter is not sending a group scheduled event or publishing his/her busy time. If we think of the CA as the "user" it also doesn't make much sense because we're not using VFREEBUSY.
The fake ORGANIZER format used by Opencast can cause problems with parsing the feed for some CAs, especially when the presenter name includes quotes e.g.
ORGANIZER;CN="abc,Some "long" presenter name goes here":mailto:abc,Someemail@example.com
This both has encoding issues (quotes within quotes) and also a non-compliant overlong line.
So simplest is just to drop ORGANIZER, as it's not meaningful or useful and can cause problems.
CAs that need the presenter info should get this from the attached episode.xml.