i regularly play (like, every day) a skilled olimar, and he switches up his game quite a bit. also, battlechrist has a few instructive videos of his TL vs. olimar in the TL video thread. anyway, here's what i have:
if he starts spamming pikmin (especially doing sh throws), stay back from him and do a flurry of sh bairs. this will kill his pikmin incredibly fast, and if you're fast enough, even if they attach, you can actually keep them to doing 0 damage. when you kill enough of them, he'll have to pull some out. however, don't just charge blindly here, because he'll be able to shield+grab you or spot dodge+dsmash you fairly easily, which will just generally piss you off. instead, take it as an opportunity to draw a bomb, do a SHDA (if you know how), and throw the bomb from a short or full jump. the arrows here will get through, and the bomb will cause some serious pikmin-genocide if it hits just right. at this point you'll want to charge him, approaching with nairs or bairs if you can, or running in and doing a spot dodge or shield. usually by this point he will be flustered enough to give you the mental advantage. the olimar i play usually doesn't spam pikmin anymore.
if he's rush+shield+grabbing you, be sure not to get caught with him next to you and you in the air. his range on his grab is good enough to get you every time you land. this is where SHDA really shines against olimar (as long as you're at medium-to-long range by the time you release your second arrow), as it prevents his rushing. but another thing i've found extremely useful with the boomerang against olimar: instead of throwing it directly at him, try throwing it about a foot above his head so that it both avoids his pikmin and, on its way back, its path will cross his. this is especially good for setting up charges, because he'll either have to shield, spot dodge, or get hit by the boomerang on its way back, and whichever of these happens, you can know exactly when it's coming.
the olimar i play doesn't necessarily edge guard (since olimar's recovery is awful), but a lot of times he'll stand about 4 feet away from the ledge and start doing his fmash toward the ledge, jumping to do his fair if i try to jump them. if he's doing this, i like to drop off the ledge, pull a bomb, and then jump back and bomb, boomerang, or arrow him. this is kind of dangerous, but it can succeed in drawing him off the ledge (which is a matchup you should win 90% of the time) or backing off. oh, and while we're here: olimar's game off the ledge SUCKS. edge hogging is extremely easy against him, especially with TL's hookshot, and if you drop down to try some KO aerials, if he tries to aerial you, a lot of the time he'll end up falling too far for his pikmin to grab hold.
remember, projectile spam can be a good thing against an overly defensive olimar. mix up their ordering, but try to do your arrows and boomerang with a bomb in hand, so you can do quicker and trickier projectile combos. it's very difficult to take olimar on a straight offensive ground or aerial game, since he has the pikmin barrier, he's so **** short, and his up+a and dsmashes have good priority. the trick is frustrating him, approaching SMARTLY when he's drawing pikmin, and using projectiles wisely.
hope that helps.
