In theory yes...but in my world, the machines are old, and abused.
if they ran plain hydraulic oil (per the book), and there's dirt settled in the tank (like from the filler port)
Changing to detergent oil is gonna bring that all up (and aren't most filters on the return side ?)
Most machines have a return filter, many also have a charge filter which is after the gear pump but before the piston pumps. Gear pumps are pretty tough, piston pumps are sensitive, getting the dirt out before them is most important.
Some hydraulic fluids are designed to allow contaminants to settle in the reservoir. In something like an SSL though it's not as practical because the reservoir is small and the oil doesn't spend much time there. Some hydraulic fluids have detergent additives. The downside to them is that they tend to emulsify water.
Foaming is one potential issue with engine oil, can cause cavitation and such. Switching to a detergent oil after years of non can really clean things up and cause some issues too. That said though, our NH machines always called for 10w30 in everything and that what they got. Have one with over 10,000hrs and never touched the hydro system. Others were ran to over 5k without issues as well.
The Cats want 10w Hydo so that's what I put in them especially since they're under warranty. We really don't go through that much and it's not that expensive. Cheaper than the smurf juice NH wanted for the newer machine we had. (they did state you could flush it for 10w30 though).
Then there's THF/UTF tractor fluid. It's a hydraulic fluid but designed to be compatible with wet brakes, ptos, etc. It usually works in place of an anti wear oil, but is more expensive. Regular AW shouldn't be used in place of UTF on something that needs UTF though. AW oils are designed for straight hydraulic system use. UTF is designed for both hydraulic and transmission/brake/clutch/etc.