Does 芋頭 have a different pronunciation in Taiwan Mandarin vs Mainland?
This is actually one example of a more general phenomenon. Mandarin, as spoken in Taiwan, uses weak stress (the neutral tone) much less often than Mandarin as spoken in northern areas. This is true not only of Taiwan speakers, but of other areas as well.  According to Jerry Norman's 1988 book, Chinese (p. 149):


  Weak stress (neutral tone) is an essential feature of the standard
  language, and of most northern dialects, but because its occurrence is
  lexically determined it is difficult for non-Peking speakers to
  master. Speakers of putonghua from many regions in South China,
  however, employ only a very small number of weakly stressed syllables,
  and these are chiefly limited to grammatical suffixes and particles.