High Current DC LEDS Strips with Aluminium Plate... is grounding advisable?
Thermal resistance from LED junction to surface is degraded by the adhesive tape but for alum plate heat radiation from SMT soldered to MCPCB I use 5sqcm/W for40’C rise in heat sink which means junction is hotter.

You have 2400 sqcm/ 170W or about 3 times this but a thermal resistance from 2 sided tape that may increase Rca thermal resistance much more than chip to copper so the the alum sheet won’t be as effective but will reduce the junction temp by the rise in sheet alum.  Since MTBF is doubled by approx every 10’ drop in junction rise (assuming no process faults) a 30 ‘ rise in metal temp translates to about an 8x improvement in lifetime, so good plan.

Now to the electrical ground or not question.

Will the SMPS radiate Common Mode RF noise? ... probably .. will that interference with high impedance sensors? Maybe if you have any.   

Will touching the plate conduct ESD interfere with anything?  Maybe but probably not 

Will it be a safety issue to ground it or not?  Not if the supply is certified but if it has a line filter, leakage current caps may be felt (200 uA approx) if you also touch this with one finger and earth ground.  So earthing it is good but does not limit ESD current which might only pose an issue if you had some long wires to some remote drivers controlling it.

So there are tradeoffs and if there are more unknowns in this system then the answer may be more complex (RC shunt to earth). 

But if it a simple horticulture lamp in high 
humidity it may be a simple answer . It doesn’t matter but compatibility issues may arise if there are other unknowns like a ground fault on other equipment or AM radio interference so earthing it is my 1st choice. But if you also have ESD sensitive electronics nearby then a 1M resistor in series is commonly used. Then if RF interference is a problem on AM radios or sensors then a 10nF cap to earth ground with a 100 ohms in series to limit ESD current.

These are my EMC thought processes to any    large ground plane with potential compatibility issues or NOT.