No, not really. Even though a crockpot may seem safe and appear to have no exposed heating element, the appliance could still potentially spark and ignite your flammable solvent.
If you want to heat your basified mhrb/solvent mix, I would suggest heating up water in the crockpot (or elsewhere) and then putting the jar containing your extraction in the warm water in another pot/container (make sure you have a thick container, like a mason jar and be careful and make sure to warm the extraction vessel at a slow, even pace so as not to crack the jar).
It may take several rounds of heating/changing the water to achieve the desired temperature, but it is the safest and least risky way to achieve what you are trying to do, imo.