do prokaryotic DNA sequences contain enhancer elements
other than the UAS(upstream activating sequence)
The Gal4/UAS system is borrowed from yeast, a eukaryote https://en.wikipedia.org/wiki/GAL4/UAS_system
In addition, are enhancer elements like promoter-proximal elements and enhancer elements encoded directly within the DNA?
Yes. Enhancers are usually considered to be encoded directly within the DNA; e.g.: see the following recently published historic perspective on the discovery of enhancers by its discoverer, Walter Schaffner : https://www.ncbi.nlm.nih.gov/pubmed/25719310
Sidenote: Enhancers have originally been discovered in a virus, and thus neither in prokaryotes nor eukaryotes
Or are they proteins that attach themselves to the strand of DNA in order to enhance transcription?
Enhances (often / ~always) exert their function though proteins. https://en.wikipedia.org/wiki/Enhancer_(genetics) Note that this doesn't necessarily affect the definition of enhancers.