major blood vessels run down either side of your tongue but not the center. in some occasional cases there are blood vessels (minor ones) in the center. cutting them really isn't much of a problem.

and you aren't splitting the muscle of the tongue. there is a band of tissue that passes through the center of your tongue (the lingual frenulum) and seperates each side. your tongue has a seperate muscle down each side. if you place a finger on the top and a thumb on the bottom of your tongue and pinch them together while you flex your tongue you can see that the center of your tongue doesn't flex upward like either side. you can feel where the two muscles meet one another in the center.

i hated having my tongue pierced. i've had it pierced several different ways and with multiples in it at the same time as well. didn't like any of them. my last piercing was at a 0g initially (scalpeled to) and that is what i cut back to whe ni actually did the split.