How are centromeric/telomeric regions categorized in RepeatMasker? "Other" category? I haven't been able to find the following in the documentation at http://www.repeatmasker.org/ 

(1) Why are certain regions classified as "Other"? Are these regions impossible to concretely classify due to alignment issues?

(2) I believe that centromeric and telomeric regions would be classified as tandem repeats. Are telomeric/centromeric regions classified as "DNA" within the hg19 version of RepeatMasker? 

Are these documented somewhere?
On (2), centromeres and telomeres primarily consist of satellite sequences. In human centromeres, the dominant type is alpha satellite (aka alphoid). GGAAT micro-satellite (aka SATIII centromeric micro-satellite) is also very common. There are less common types such as beta satellite. Because there are all kinds of centromeric/telomeric sequences of different lengths and properties, RepeatMasker doesn't put them into one class. Note that RepeatMasker has a "centr" class but it does not include all centromeric satellites (no SATIII, for example). In general, it is not advised to find centromeres with RepeatMasker output.

GRCh38 is an unusual reference genome in that its centromeric sequences are computationally generated modeled after Venter as I remember. They are mostly alpha satellite, but are not real sequences (which has always bugged me). GRC know exactly where they put these sequences. GRCh37 is a more typical reference genome. It lacks probably majority of alpha satellites, but still has many. When you map reads to GRCh37, you occasionally see ~10,000-fold read depth even though the average depth is ~30X. These regions are mostly alpha satellites. Mappers just pile all different copies of satellites onto the ones remained in GRCh37.