I got a very similar 220V COB from eBay for £3.50 (for some reason cheapo chinese parts cost far more on eBay here) but it is 100W blurple. I fixed it to a CPU cooler and it seems fine, if a little hot. When I go back I will fit a fan of some sort to it
I am seeing what it runs like with some chilli plants before I do anything important. The basil found it too much but the chilli plants like it. They are a nice dark colour and are flowering nicely.
I would say not only can you, I would highly recommend it. Earth anything made from anything conductive that you may touch.
Remember, earths are there for when things come loose so don't just earth places connected to powered devices (like your COB and the tray), earth anything made from metal or other conductors that you might either touch during normal use, or need to touch to take things apart like any framework you may erect.
I would run the live and neutral to your cob then run the earth wire to your baking tray making sure to connect to bare metal, not whatever is coating the tray, and also run a nice thick earth wire to any metal parts you may be using.
EDIT : Also get some CPU heat sink paste (TIM : Thermal Interface Material) from a computer supply place, it will allow far more heat to conduct from your COB to your heatsink.