There were some concerns raised earlier on that the Open XML format required a specific object embedding to be used (OLE). While it's true that the tag names in the format have "OLE" in them, the embedding is actually generic, and can use other technologies if that's what's desired. I believe (but I'm not positive) that this is also true for ODF's draw:object-ole element.
Eric White has a blog post that demonstrates how to embed a KPart on a Linux machine and store that in the Open XML format: http://blogs.msdn.com/ericwhite/archive/2008/03/10/spreadsheet-simulation-demonstrating-an-embedded-kpart-on-linux.aspx
It's pretty cool… he created a mini spreadsheet application that reads in an xlsx file with an embedded HTML viewer KPart. The application displays the values in the cells, along with the embedded object.