Just installed an Omega rail 7.0 on my carbine - do I need to rezero?

You will need to put some rounds down range on paper to check zero. I have had some shoot the same after changing things and some shoot way off to just a little.

A. Yes, shoot to prove zero.
2. Besides, shooting is fun; thus any reason to go is a good one. Use it.
III. in any system, repeat-ability is limited by the number of changing variables. Scope-to-mount is one variable. Mount-to-weapon is another. The mount creates the baseline by which you measure the performance of such sights as you mount. You have changed the baseline, ergo you need to recheck the result.
Which ought to be a fun occasion anyway, see above. Rinse and repeat. Your mileage may vary.

Of coarse...

The fact that you felt the need to ask the question pretty much answers it.

Even though your sight is receiver mounted, changing the forend is likely to change your zero. The whole point of a free float is to eliminate pressure on your barrel that can affect zero.
Removing the stresses that you had before is going to change how the rifle shoots, particularly when fired from a rest or with a tight sling.

You may or may not need to rezero, but you definitely need to CHECK your zero before using it for hunting, match or possible defensive use.

Definitely verify. If for no other reason, than to eliminate your doubt. Use it as a handy excuse to go toss some lead down range.