Yes, this is true, but there are more reasons for spaying or neutering a rabbit. A female really needs to be spayed between the ages of 4 to 6 months. Unspayed females are prone to developing uterine and ovarian cancer, usually between the ages of 3 and 5 years, if they're not spayed. I'm permanently fostering an older rabbit who had developed uterine cancer before the rabbit rescue got her. We removed the cancerous uterine and ovaries a few months ago. Now, we're waiting to see if we got all of the cancer or if it spread to other parts of her body, like the lungs.
While spays are expensive, I've already spent more than 4 times the cost of a spay taking care of her cancer.
Males can develop testicular cancer, although this is not as common as uterine cancer is in females. Neutering a male is not as expensive as spaying a female, usually. It is a much less invasive surgery and the boys recover pretty fast. Neutering will help stop the boy's (and girl's) tendency to spray their area with urine to mark their territory. Also, the boys are much less frustrated after being neutered. An unneutered adult male spends a great deal of time and energy looking for a "mate". I "bunnysat" an unneutered adult male who fell in love with my forearms. Within a couple of days, my arms had alot of long scratches and bruises from his attention. I looked like a failed suicide attempt. I felt very sorry for him, though. He was a very sweet rabbit, but also an extremely frustrated rabbit.
Getting your rabbit desexed will also help a great deal with their litter box habits for both boys and girls.
It would be best for you and your rabbit to get him or her desexed. Your rabbit will not be so territorial and aggressive. The rabbit rescue I volunteer with often gets rabbits who the prior owners says are aggressive. But, really, they're not. They just need help controlling their hormones.