Yes there are some cam cleats that can take direct loads from mainsails, etc. but you have to work out all the potential loads involved, such as the 'mechanical advantage' of your block system of your mainsheet to insure that you dont go beyond the inherent strength of the cam cleat.
If the force of the lines given to the cam cleat is too great you may have great difficulty in releasing; "trigger" cam cleats can then work - the cam cleat has a 'trigger' that when the rope is pulled down onto the trigger which automatically opens and totally disengages the cleat .... but the high loads will then transfer to your hands and arms, etc.
The Harken website has a 'calculator' for you to analyse all the loads involved and can pretty well match those loads to most of their equipment. If thats not possible, then simply call/contact the hardware manufacturer's *application department* and they will make the appropriate recommendations; best is to send a drawing or picture of what you intend, including your boat detail description, etc. and the wind/wave conditions that you normally intend to sail.
Anywho .... for direct mainsheet to cam cleat, I prefer to run the line through a *hexaratchet* before the line enters the cam cleat .... prevents rope-burning your hands if the loads at that time of release are greater than what you can 'hold' .... the hexaratchet then is able to 'snub' the line for you (as would with a winch, but you have to always 'wrap' the winch) and with little to minimal hand pressure on the rope. The hexaratchet is 'always' connected and engaged and thus needs no mechanical 'wrapping'.
I use hexaratchets on all control lines that could possibly give me 'rope burns' ... mainsheets, jib sheets, furling drum control lines, etc. .... downside is they're not 'cheap'.