The lie angle needed for Symple Swing is the same (standard) as for any other swing.
The swing plane is defined by three points (the ball, your left shoulder joint, and the target.) The swing plane therefore is the same for all swings UNLESS the other swings have a radically different stance that raises or lowers the front shoulder at impact. (I haven't seen any swings that vary that radically)
When I was a Natural Golf certified instructor I asked everyone I could find at NG headquarters why they recommended more upright clubs. No one could give me a straight technical answer. They all started sputtering nonsensical marketing babble. Yes Natural Golfers stand with their hands very high at address but that doesn't have any real effect on their impact position. If you look at a Symple Swinger, a conventional swinger, and a Natural Golfer at impact their positions are pretty much identical except for minor grip variations and stance width.
I hope this answers your question. If it doesn't please feel free to ask again.
I was fitted for a set of irons a couple years ago and the fitter convinced me that I needed an upright lie. I hit them ok. I recently bought some new irons with a standard lie. I hit them ok too. I just make a minor adjustment at address and i can hit either set of clubs equally well. I really don't know what this says about SS or club fitting, just thought I'd put it out there.
You might need an upright lie. If you really do need an upright lie it's likely that you're taller than average and/or have an upright stance. Those things would increase the height of your front shoulder joint necessitating a more upright lie angle.
I have seen disreputable club fitters tell golfers that they need something special (upright, flat, or whatever) just so the club fitter can position himself as "savior" to the golfer.