Honestly, if Robert came along with some other more desirable units then in that situation I wouldn't reroll. I say this cus if you want to later do Toast to Men G you will need as many male healers as you can get since they are desperately needed there.
But again, this would be if Robert was a consolation prize for having got some decent plat and/or black units. If he was the only other worthwhile unit you got, I'd say reroll and see if he pops up again alongside some higher tier units.