Went ahead and watched the first, last, and 2-3 other matches against you (ESAM), and here's what I noticed!
Some of the Pikachu matches are tough, I'd say a good 100%+ in some of the matches was from plucking his own grenades and them hitting both of you. I might be wrong on this too, but if I look at all the moves that hit from the final match (until the end of your first stock, coincidentally the start of his third) it was pure grenades except for one f-tilt near the beginning, an up-tilt that didn't kill, and the forward throw that finally did the job. That's over two lives of his, and the third ends in an unfortunate quit after a d-throw chain.
He has more options than he thinks, is all, he's just got to explore a little more variety. I noticed if he's camping you off the edge or just if he has time to in general, he'll pluck both grenades and get rid of them immediately. It might not be a bad idea to keep one in his hand even, Snake can still move forward or backward, and more importantly, he can cook them. Grenades, to me, are every bit as good for stage control as they are for damage, and if he can predict a double quick attack left (with the right covered by grenades, C4, whatever) he could potentially change the flow of the match. I was praying hard for the best sometimes, but he just couldn't keep the pressure on with those grenades.
I also saw only one DACUS in the four games against Pikachu I watched, minus one that was interrupted before the mortar came out. Pikachu's quick and spends a lot of time in the air, it's not a bad option, increases Snake's mobility and throws out a protective missile at the same time. It's situational, sure, but it doesn't seem like a bad idea.
C4 usage wasn't too good, in the fourth match against you, he plants one right away in the center and it blows up on him (timer runs out) at 0:29. He potentially had a few chances to detonate it, and he definitely shouldn't have let it blow up on his own. Also, I'd probably try to plant it on the platform on the left side (this one's on Frigate Orpheon) or the one on the right, it helps fence out part of the stage and keep the opponent on their toes, and cut off even a little bit of Pikachu's mobility in that quadrant. Watch 1:04-1:10 or so, he's just dropping and detonating.
Tech chasing, in every case I ever saw, was either a jab or an up-tilt after the initial down-throw, if not waiting in shield for a nearby grenade to blow up. If the opponent buffers a tech roll to the left or the right, nothing happened. If he's a quick thinker, after the down throw, he can shield and if the opponent doesn't roll away from him he can either shield through the getup attack and regrab/f-tilt or f-tilt behind him, that's an easy 30%, he can take advantage of those down throws a lot more.
This one's important, I think, because it's simple and he can change it immediately for great results. When recovering with his Up-B, he comes in low straight back to the stage, and he's defenseless, it was free damage every single time. The best instance of this is in the fourth video against you,
http://www.youtube.com/watch?v=vpfBB-il50g , around 1:08-1:25. If you watch from 1 minute on, he Up-B's low and hard horizontal into the stage, where he gets forward smashed, b-throwed, n-aired, and thundered in quick succession. That's a ton of damage. Use the C4, whatever you have to do, if you're in doubt Snake should come in high. I've seen him wavebounce the grenades, so he'll do much, much better avoiding you, he loses 60% that way before being set up for a lethal up-smash.
He's definitely not a bad player, some very nice matches out there, went head-to-head with some great FL players. Hope some of that helps, though!
Edit: I went ahead and watched a couple vs. Seibrik, and those went a lot better! haha seriously, he's a good Snake!