Yes, communication towers should be grounded for the following reasons:
o Dissipate lightning current to bulk earth
o Reduce potential differences between parts.
o Minimize the electromagnetic coupling to reduce electrical noise.
Tower are not isolated, the antena site typically is connected to electrical and electronic devices some of then are even direct mounted on the tower such as strobe lights, lightning mast and antena direct connected by cable to a shelter that house electrical and sensitive electronic equipment.