Do you have a dedicated teammate? The way I see it, if you would be happy with being as good as PewPewU and SFAT are in teams, you'll be fine playing Marth. However, Marth more than any other character imo benefits from having a dedicated teammate, as it's really important to have a strong understanding of what the Marth player is going to do if he's on your team.
Personally, I don't like Marth that much in teams because of two things. One, his moves require a lot of precision to be effective, it's not like a Fox or Peach where you can just throw stuff out and if it hits you're good. And two, he has a lot of trouble pushing people out of his way. Like, a Falcon or Fox can get from the left side of the stage to the right side pretty much regardless of what's going on in the middle. Marth has to be very careful about who he's going around and how he goes around them. But neither of these are crippling issues, they're just things to be conscious of when practicing teams.
Marth also does especially well with certain characters imo. I will never, ever play Marth/Puff, and rarely will I play Marth/Sheik or Marth/Falco. I really only like him with a "bully" on his team, ideally Fox, but Falcon or Peach can work well too. You want someone who can get in there and 1v2 while you poke at the brawl to keep things favorable for your side, as well as continue combos on characters sent your way. At least, that's my playstyle as Marth in teams.
So to answer your question, yes, Marth is fine in teams. But he will probably take more work than another character, and doing pickups will be noticeably more difficult. Hope this helps