Yes, the words added to a company-wide custom dictionary are case-sensitive as the system compares the exact string in the dictionary with the word entered in the text field.
However, an added lowercase word will be considered correct also while writing starting with the capital letter and in CAPSLOCK. For example, you added the word 'xxxxxx'. Thus three writings will be correct: 'Xxxxxx', 'xxxxxx' and 'XXXXXX'. Note that the opposite situation when you add a word starting with the capital letter 'Xxxxxx' will NOT work for other cases: 'xxxxxx' and 'XXXXXX'.
