Good article. I do not have a negative view towards arbitrage. As you've stated, this is not front-running, as has happened in the financial markets, rather:
- advertisers have a chance to participate in any auction they like, cutting out the arbitrager
- the publishers win with a higher % of sold inventory
- the exchanges (RTB venues) win with additional transaction revenue
Arbitragers, as opposed to HF "gamers", have had a useful function in the financial markets, keeping prices consistent and "fair" for different participants coming through different venues. If the short-sell existed in this market place, one could even seen an arb pushing inflated pricing on one venue down as is done in financial markets.