My opinion is that it would be best to omit the decimal point in the diagram. The labels --Ones, Tenths, Hundredths-- get the point across. Trying to include the decimal in braille seems like it would be a distraction. HOWEVER, following the Tactile Graphics Guidelines, your layout probably will not be in table form. If you are showing the table vertically, you could insert the word ..decimal.. (enclosed in transcriber's notes symbols) between the Ones groupings and the Tenths groupings.
Regarding the blank tables for students to do their work, I expect in the classroom they will be working with counting blocks. ..Ask your teacher... would be an appropriate TN here.