Are there any negative effects of getting too little REM sleep?

Maybe. Human growth hormone (hgh) is particularly released during delta phase of sleep, the deepest sleep level. In an adult, hgh is involved in many pathways involved in maximum tissue and organ performance and minimizes age related breakdown. Remember, it is not necessarily total sleep time but more so the quality and level of delta sleep levels that may be at play.
Yes. Rem sleep is a part of the sleep cycle that is restorative for the body. Usually during this part of the sleep cycle the body gets a chance to recover . If you are not getting enough ram to sleep during the night this may result in significant daytime sleepiness and a lack of restfulness. Medications can decrease rem sleep and patients with sleep apnea usually have a decrease in rem.