That MU isn't that bad. At the worst its 45-55 for Snake. The roadblock that most Snake's encounter with this matchup is that they're too aggresive. You need to play VERY safe and your spacing needs to be correct as well. Olimar, like Snake is a ground combat character but has better spacing options with his **** grab range and red pikmin that don't die from explosives.
Your grenade game has to be on point here and you have to be very patient. Pay very close attention to what Pikmin he has in front and which one is second. Olimars often like to bait players with obvious grabs and then punish them accordingly with the next Pikmin. Remember:
Red - Immune to fire damage (your explosives), their aerials kill. They are always the first Pikmin called to the front when Pikmin Whistle is used.
Yellow- High priority, creates disjointed hitboxes, their spikes are lethal, quick and disjointed. Their Up airs juggle well also. Next in line after Red.
Blue - Extremely long grab range and great grabbing power. Average in all other aspects. Next after Yellow.
White - Quickest grabs and their range is about as good as blues. Their overall power for KO, grabbing, damage is very weak. When they latch on to you though they do the most damage. 40% if uninterrupted.Oh and their pummels on their grabs do a lot of damage too 3 to 4% each hit. Next after Blue.
Purple: Their grab range is horrid. Olimar won't be grabbing you with this unless your within KO range most likely. They don't latch on when thrown they just turn into decent knockback projectiles. Due to their weight, their Up Smashes and Up Throws are LETHAL. Remember this. Also they live longer than other Pikmin.
Know how these affect Olimar's playstyle. What seems like a random, erratic playstyle is actually somewhat telegraphed for you.
Okay anyway, play smart, and I reccomend saving Up-Tilt if you can. You want him to die asap as he racks up the damage insanely fast on you. Don't get demoralized if you get comboed for 60%, it can happen easily. Camp with Nades effectively and wait for your opportunity. When you gain momentum don't give up. Olimar succumbs to pressure much like Snake does.
And if you can land a grab on him its very valuable. It's not hard to tech chase him at all but at the very least get him off the stage. B-Throw, F-Throw, whatever.
EDGEGUARD. Not enough Snakes do this. He has a tether recovery!! Get him off the stage and make it hell for him to get back on. He can be gimped if you're smart.
If he gets you off the stage and you have to get back on it don't get predictable. Pivot grabs **** predictable Snakes and then you're flung off the stage again. B-Reversal your specials, soft throw grenades, drop C4, just switch it up. You don't want to be grabbed here at all.
There's more but I'm at work and feeling lazy. Hope this helped.