They are the same as in "the rules are the same". The difference is mostly about liquidity, so their prices will move easily, therefore are easier to manipulate. It sucks, but at least in cryptocurrencies there is little that can be done because there is no regulations.

Yes, the PS was actually to @ecoinstar (forgot to tag him). The way he wrote it seems like it's all the same thing. If anyone else reading this still have doubts:

Spread trade - Act on high spread markets, looking for profits due to the buy and sell order prices.
Arbitrage - Look for profit on the difference between prices of different markets (buy in one and sell on the other at the same time). They don't exaclt provide liquidity, because they act on the market taker side, because they need to move fast. So they actutally remove liquidity
Scalper - Looking for profits due to small price movements during the day. They go in and out of a trade really fast, and usually only act on markets that allow margin trades (leverage).