Yes, inhibiting sub-vocalization is likely to impair comprehension.
Here is the abstract from Slowiaczek & Clifton (1980):
Two experiments demonstrated that subvocalization is of value in reading for certain types of meaning. Blocking subvocalization by requiring subjects to count or say “cola-colacola …” aloud impaired their reading comprehension but generally not their listening comprehension. The effect of blocking subvocalization was found to be specific to tests that required integration of concepts within or across sentences, as contrasted with tests that required only memory of individual word concepts. Two hypotheses were offered: first, that subvocalization results in a more durable memory representation needed for integration of concepts; and second, that subvocalization enables a prosodic restructuring that makes information needed for sentence comprehension accessible.
Slowiaczek, M. L., & Clifton Jr, C. (1980). Subvocalization and reading for meaning. Journal of Verbal Learning and Verbal Behavior, 19(5), 573-582.