I noticed when opening an Excel file with the JMP Excel add-in, Boolean values get imported as numeric, but if opening the Excel file through the Excel Import Wizard or copy/paste from Excel to JMP, the Boolean values become text. Converting the numeric values to text is straightforward enough through Recode column utility or using a formula.
Ex. dt << New Column( "Boolean Text", Formula( if( :flag == 1, "TRUE", "FALSE" ) ) );