Can I put a 600w hps in a 6x5 grow tent without having heat issues? Also, is this adequate enough light to pull off 1 gram per watt?
No problem with a tent that size. 1g/watt with 600W and a tent that large will be difficult to do. I'd step up to a 1000W or not use all of he space in your tent.
I still think this is marginal, 600w in 6x5 will need an extract fan, although the fan may not need to be on during winter depending on location as for the 1g/watt thats up to you, strain, system to grow in ...? and other variables