I would. It is my personal policy that drives should be kept under 40C if possible. Most drives are only rated to operate to 55C, although some can go as high as 60C. Temps over 40C will probably cause a reduction in the life of the unit, and temps over 50C will probably reduce service life significantly.
A single 92mm fan in the front of my case, on the lowest speed my fan controller will allow, keeps my WD2500KS in the low 30s That is a 10C drop from when the drive was simply sitting in the open during open air testing, but without a fan.