^^^Agree^^^ (even if it is safe for your recorder) - Way too risky to plug into passive speakers - you could really screw up the whole show if you had a bad cable or such...or turned on phantom, etc.
This "secret" approach is really best for small bar/club taping where you know someone in the band and/or permission and easy access to the connection. (like the speaker is right next to you table.)
Also - should make sure your patch cable is taped down with no possibility of a trip pulling the speaker/stand over.
I am friends with the owners and the promotions guy, he actually gets me all the permissions from national bands to record, so I won't have to worry about permissions, typically he has me come in 2 hours before doors to set up cameras so that will give us ample time to try it out at the next soundcheck before a show.
I feared there might be repercussions/risks that's why I asked, so I will use extreme caution and see what happens at the next soundcheck.
alternately, I do have the speaker specs so I could replicate the scenario with my speakers at home that are the same ohms and receiving a lot of power. if it's a hit or miss I will post that info back here once I am sure the results are consistent.