I have stayed several nights in Venice and thoroughly enjoyed every minute. The atmosphere totally changes as nightfall arrives and all the day-trippers (those staying on the mainland, cruise ship passengers and coach tour visitors) all depart. Wonderful.
August wouldn't be my first choice for visiting Venice but I understand if there are time constraints. Just make sure the hotel you choose has A/C. Although, it will probably be configured to automatically turn off when you are not in the room...
If you are planning several nights in Venice, you might consider an apartment over a hotel room. Many times, the price is comparable yet an apartment can be much more comfortable and convenient. I think Venice is delightful for a week or more as once settled in, it can be fairly economical and there are so many sights to see in a short commuting distance when you feel the need to escape the crowds in the lagoon. Vicenza, Padua and Verona are all a short train ride away and there are plenty of escorted day trips into the countryside and mountains to choose from.
The key to Venice is to sleep and eat as far away from the tourist centers as possible. The further away from Piazza San Marco, Rio Terà Lista di Spagna, the Grand Canal, etc. you get, the higher the quality and the better the price. The rule of thumb, if you see throngs of tourists streaming past, it's probably a tourist trap.