As long as the unit is operated in a room where the ambient temperature meets the published specification, the electronics and the fan should automatically manage the internal temperatures - the fan will turn on, off, and change speed as required.
As the room temperature rises, so will the internal temperature, and it is conceivable that at some point, if the room gets hot enough, the internal temperature will rise to a point that becomes dangerous - and this is likely to be more of an issue for the disks that the unit's internal electronics.
If it will make you feel any better, set the temperature warning at or a few degrees below the upper limit for your disks and it will shut down when the threshold is reached.
I've been running my DNS-323 with this at the default for over two years, 24/7 operation, in a room where the ambient is always 80+, idle temps run at around 110, operating temps approach 120 - I have yet to lose a disk.