The dimension type can be found via following function:
gSDK->GetObjectVariable(dimObject, ovDimClass, TVariableBlock)
The mapping of the types can be found in "MiniCadCallBacks.h", as well as other specifiers (e.g. ovDimFontStyle) , if you are looking for other properties of the dimension object.
// (fix_ang) = 0,
// (sloped) = 1,
// (ordinate) = 2,
// (radial) = 3,
// (diametrical) = 4,
// (ang) = 5;