Aruba is generally a very safe place at any time of day or night. However, it would probably be wise to stay away from the area surrounding the Valero refinery on the southeast part of the island at night in the words of a Valero employee, "you will get some undesirables down there at night". There is generally no reason for a tourist to go there at all anyway, so this likely will not be an issue.
While rarely enforced, all drug abuse - including cannabis - is illegal.
Also be aware tourists have been targeted, and there have been many stolen cars recently. In the Malmok beach area, just beyond the high rise 5 rental cars were stolen in 1 night Read this article.