The example on Wiktionary uses brackets (http://en.wiktionary.org/wiki/i.e), and the at Answers.com all the examples show i.e. used in parenthetical expressions of some sort (bracket, comma or em-dash) (http://wiki.answers.com/Q/When_to_use_ie_in_a_sentence). So I would suggest it is probably a good idea, particularly if there is some doubt as to where the restatement ends and the rest of the sentence begins.