As long as you are leaving your abdominal binder in place as your surgeon has prescribed (It should be on nearly full-time, only off for dressing changes, drain stripping and cleansing, and adjustment to avoid wrinkles and bulges), using lotion for dry skin--not on incisions--is perfectly fine. Vitamin E as skin lotion is probably of less value than Lubriderm, Nutraderm, Eucerin, Vaseline Intensive Care, etc., but as long as you keep your incisions clean and dry, the skin lubricant you chooses is relatively immaterial. You should generally avoid lotions heavy in perfume or alcohol content, as these can actually irritate and make your itching worse.
Part of your itching may be due to skin sensory nerves healing and regenerating, so lotions won't really help this aspect.
As for Vitamin E and scars, I agree with my colleagues that there are no credible studies that show a clear-cut statistical advantage in Vitamin E scar treatment. However, scar massage and scar pads have been shown to offer some improvements in scar quality and maturation, so I say why NOT use Vitamin E as the massage oil? However, Vitamin E, cocoa butter, or other massage lotions are less important than the actual scar massage!
Also, some surgeons who use drains with tummy tuck patients prefer that the patient not shower while the drains are in place to help reduce the potential for introducing bacteria via the drain site in the skin, so check with your surgeon about bathing (showering) recommendations. Best wishes for a speedy recovery and a great result!