Can I add product scope Custom Dimensions in App+Web Ecommerce data?

Currently, product scope Custom Dimensions are not supported by GA App+Web.

Which events can we use to send items array for App+Web Ecommerce tracking?

You can send items array with the following events

Event NameEcommerce Activity
view_item_listProduct Impressions 
select_itemProduct Clicks
view_itemProduct Detail Impressions
add_to_cartAdd to Cart
remove_from_cartRemove From Cart
view_promotionPromotion Impressions 
select_promotionPromotion Clicks
begin_checkoutCheckout  – Step 1
add_payment_infoCheckout  – Add Payment Details Info
add_shipping_infoCheckout  – Add Shipping Details Info