Front running large equity programs is legal with the use of stock-index futures because each product is regulated by 2 very different regulatory agencies. Furthermore, most equity-derivative desks will "run in front" of an equity-program buy/sale with the use of index-futures because they just made the customer a bid or offer and are trying to hedge themselves of the risk that they have, having just assumed the clients position, which they will seek to unwind over the next few minutes, depending on what their view of the market is. Thus, the desk will make commissions on the program trade, +/- any of the "unwinding" of the position.
Front running stock on an equity trading desk with stock is totally illegal, and I believe in many cases the use of equity-options to front-run is also illegal.
Hope this helps answer your question.