Today I picked up some Black Gold Sphagnum Peat from OSH and used it to start some sphagnum cultures. It says the only thing added is an organic moisture control agent, which is some sort of extract, I forget. I think it sounded like Tecca or something, I forget. It is organic, not a chemical. So I'd say that is perfectly safe for sphagnum and CPs.
Personally, I think even MiracleGro is perfectly fine with a rinse. All it has in it is a bit of fertilizer. They spray a tiny bit of diluted on just enough so they can say that it is on there and that it will help your plants. The fert level is 0.10-0.05-0.10... The fert level in fertilizer that I use foliarly on my Nepenthes is 16-16-16.
Coffee, a common fert used for Nepenthes, has a fert level of 2.0-0.3-0.2... That is a LOT more than in the MiracleGro peat. You can just rinse coffee out and everything is okay again. You should be able to do the same for MiracleGro.
A lot of others will say that you should not and can not use MiracleGro peat, but I have used it with amphibians with NO washing. I also have used MiracleGro perlite which has more fertilizer than the peat even. I just wash it. I have used it in all of the Nepenthes that I have repotted, I have used it in my sphagnum cultures.
If you are really concerned, which you shouldn't be after reading this, you can buy some organic like the Black Gold I mentioned or other stuff they sell that is organic. Now you know you can go with the cheapest option and just rinse with distilled water.