Modern Vespa

So I recently put a new Malossi clutch in my GTS and have been enjoying the super smooth performance over my old stock chatterbox.

Maybe too smooth.

Today I noticed the clutch slipping when accelerating, and sure enough upon opening it up I see grease all over the bell and pads.
I guess I'm a dum dum and used the wrong grease for re-packing the moving parts on the driven pulley before putting it all back together

So my question is: are the clutch pads ruined now that liquified grease has smeared all over them? And if not, how to go about cleaning them?

If you repacked because the pulleys were dry. That's because you need to replace the seals/bearings/seal collar. Now, every time you put more grease in, it will leak out.
It's easy to ask for help and forget to reveal the mileage to help members troubleshoot.

I repacked it and replaced the seals because it's cheap and convenient to do when the whole clutch is apart, even if it only has 15k (not considered super high miles, but I have found bearings prematurely worn in other parts).

But the actual question is whether the new clutch shoes are toast after becoming greased...

I wouldn't use saturated brake or clutch pads.
I looked at the parts diagram for the driven pulley. There are two o-rings and part #833674 cup that seal the guide pins and grease in the slots. I had to replace a similar part on the Honda driven pulley at 23,000 miles. It was damaged compromising the seal.
At risk of argument, I don't see any parts in the diagram labeled a seal.

I've just had a mineral oil brake fluid leak that contaminated the organic brake pads on my mountain bike.

I cleaned everything up with Brake and Clutch Cleaner and the brake is now working perfectly.

Vespa pads and grease may react differently, but worth a try?

It's definitely worth a try to clean them up with brake cleaner and of course, degrease the bell too. Then after they dry use 100 grit emery or sandpaper to take down the top of the pads just a little. However, when doing this make sure to use a small sanding block to avoid uneven finger pressure on the clutch pads. Chamfer the leading edge of the pads too. If you alter the radius or cause even a small amount of unevenness to the friction material you will get some form of clutch judder and or noise after a small amount of mileage.

Apart from the inner clutch bearings, you don't need any grease on the clutch input shaft splines, just a little lithium grease (the tiniest amount) on the end of the clutch input shaft where it goes into the transmission cover bearing. This stops the transmission case sticking on the bearing at a later date. Make sure to keep the input shaft clutch nut threads completely dry and do not use any thread lock. Just torque to the required value.

It's possible the inner clutch bearing seal has been damaged during removal or refitting after packing with grease. That could be the reason everything is greasy. However, it may just be you have overpacked the bearings. Good luck!

I'll check the seal for damage.
I followed Robot's video advice and packed the thing pretty full of grease (happens at around 20:00)