A well-formed GEDCOM has an "Association Structure" that associates individuals to individuals. This is a level 1 tag called "ASSO" defined as follows:
1 ASSO @XREF:INDI@
2 RELA "Relationship_Descriptor" example: godson
Unfortunatelly the GEDCOM standard never incorporated this structure into the "Event_Structure" so that an event could show who were witnesses of the event like a baptism, wedding or the officiant of the event etc. Many software programs (TMG, webtrees, etc) have added this structure to the event. While I don't use ASSO structure, I put this information in a NOTE tag, I would suspect FTM2012 would drop the additional event tag.
When creating a custom fact in FTM (in GEDCOM speak an individual has events and attributes) my experience is that the fact is developed as a 100% well-formed GEDCOM event and should transfer as such to TMG. Unfortumatelly FTM2012 only creates "EVENt" structures and not "FACT" (aka attribute) structures, for example.
2 TYPE Land Lease
2 DATE 2 OCT 1837
An EVENt structure does not allow for a "descriptive value" while a FACT structure does allow a "descriptive value".
1 FACT baliff
2 TYPE civic appointment
2 DATE 2 OCT 1837
Where "TYPE" is a generic fact (similar to "birth") and the "descriptive value" is more specific. The FACT tag was added in the 5.5.1 draft release of the GEDCOM standard and is very valuable for these cases. Some programs will read this tag structure others will drop them. The FACT tag is dropped by FTM2012 (this blows I use the tag all the time), however, the EVEN tag (which technically can't have a description) does import, with and without the description.
EDIT: I'm not sure what a "Role" is, so I can't comment yet.
EDIT 2: ASSO tags are also dropped by FTM2012
EDIT 3: The biggest problem to date is that the RESN tag is dropped by FTM2012. This is the "Restriction" tag used for privacy of individuals and events/facts.