ShopSmith used to sell blades made specifically for plywood, but they no longer do, as far as I can tell.
If you are going to be doing a lot of plywood cutting, you might invest in a quality plywood blade from a third party, if you have a 5/8" ShopSmith arbor to mount it on. If you are only occasionally cutting plywood, a good quality combination blade can be used. Remember that plywood does not have a specific grain direction, because it varies from ply to ply for strength, but because of that, every cut should be treated like a crosscut. That is to say, you should plan on a slower feed rate, even if you are "ripping" the plywood. That is the reason for the plywood blade with many teeth or a combination blade. You would *not* want to use a ripping blade for plywood. I don't usually like to muck up a nice crosscut blade with the glues, etc. in plywood, so I reach for the combo blade.
Also, a few pointers, raising the blade higher than you normally would can help with a cleaner cut because of the angle of attack. Also, remember if you have a "good" side of your plywood, to keep the good side up. You can also use blue masking tape or other techniques to help prevent chipout when cutting plywood, if you need as perfect a surface as possible.
Last, but certainly not least, always be careful! If you are cutting an entire 4' x 8' sheet of plywood, even if it's thin, it's a beast to handle. Make sure you have plenty of table support, as well as infeed and outfeed support, double check your setup, and go s-l-o-w-l-y. A helper is always recommended for a full sheet, if you can find one. Two helpers for 3/4" stock is not out of the question (those panels are quite heavy). Personally, while I have done it, I don't cut full sheet on the SS anymore. I use a track system (TrueTrac) with a circular saw and a reasonably priced Diablo blade and do my initial breakdown that way. If you can get it broken down at the store on their panel saw or at home via some means where you don't have to push the stock through the blade, but rather can move the blade across the stock, I would recommend it. Once you have pieces in a more manageable size, the above tips on plywood cutting with the ShopSmith still apply.
1985 Mark V upgraded to 520 and Power Pro (SN 000527)
1983 Mark V Shop Deputy (SN 163487)
1982 Mark V headstock (SN 122265)
1949 (?) 10 ER in transition to dedicated drill press (SN 18677)
11" Band Saw (Aluminum Table System upgrade) (SN 34026)
4" Jointer (SN 02-18-98)
6" Belt Sander (SN 19012)
18" Jig Saw (SN 17407)
20" Scroll Saw (SN 010593)
12" Thickness Planer (SN 10406)
Strip Sander (SN pending)
DC3300 Dust Collector (SN 102088)