I think I got the impression about how bad it was, even without the all caps!
It would help to know what engines, how long, what kind of loads, what oils, etc.
Under no load, there would be minimal, if any damage. Under load...well, hydralic oil probably approximates a 20W20 motor oil...without anywhere near the additive package of motoroil. Mixed in with motor oil as a top up...well, it would definitely be less serious.
Obvioiusly, change and dump the motor oil immediately. I would, if at all possible INSIST that the oil company pay for that, and a series of used oil analyis reports to check the engine condition. If possible, make them get the hydralic fluid that was in the engines analysed also.
Even if the oil company balks, if you have to pay for the oil analysis reports out of pocket, I would still get some, espicially if you can get samples of the contaminated oil from the engine(s)...if it shows high wear metals, you'd have some serious leverage with the oil company!