Yes, the dent is fine. You just won't be able to suck up anything from below the bottom of the spear.
You will, however, need to fix the leaking seals. If it's just the in valve, you might be fine after you hook up your CO2 source, since you will have constant pressure going in. I would hook everything up and check for leaks with soapy water, and suck the water/cleaner out until empty to see how much beer you will leave behind in the bottom.