Does shooting enemies' heads in dead space making them more unpredictable?
Generally, you'll find this is a trend; yes.
Deadspace's "trope" is that "headshot's don't work" - you need to aim to remove limbs, rather than just "putting one in their skull". Thematically, if you do remove the head, this would make sense that since the Necromorphs are controlled somewhat telepathically as well, the removal of their perceptive abilities would force a more violent response - "swing until you hit something".
The opposite becomes true if you remove their limbs - one leg and on arm, and they slow down immensely.