Can als present as upper motor neuron dominant? how rare is it?

ALS: Yes, in some individuals there does seem to be a prevalence for one versus the other. At least at the beginning of the disease. As it progresses both upper and lower are progressively destroyed. Within ALS I wouldn't call it a rare finding. Its more related to the precision of the diagnostic findings by individual neurologists and overall timing.

Yes it can: One variant is called primary lateral sclerosis, and is usually expressed as spinal cord, corticospinal tract, but likely is focused at brain level, another form, progressive bulbar palsy, primarily localized at base of brain in brainstem, each about 1-3% of all ALS cases.