...
Remark (Jesper): if these kind of utilities are used in the SDK, they should be added in such a way that they can easily be replaced. Adrian explains that it is indeed the way it is set up, also to avoid that wrappers only run on Windows/.Net and not on Linux/Mono if some of the utilities are not available on the latter.
DHI right now uses a small part of the nettopologysuite. It is based on the geo api (see http://geoapi.codeplex.com). It might be that dotSpatial will also base their topology part on the geo api. If this all becomes a bit standardize we may extend OpenMI2.Standard.TimeSpace.ISpatialDefinition
OATC C# SDK/GUI
Oatc Java SDK/GUI
...