Going through a GD&T refresher course this week and one function of Inventor stuck out as being not possible to be compliant with ASME Y14.-1994 practices without manual editing. The application of a datum identifier, tagged to a feature control frame requires the triangle to be visible per the standard. Using the datum identifier check-box within Inventor from within the feature control frame edit dialog will apply the datum identifier to the feature control frame as an attached box with no triangle attachment. It seems like there should be an option within your style settings to change this to comply with the ASME standard. The only method to show this properly is to manually attach a datum identifier to the feature control frame as shown on the right side of the image below.