In the first place making two alternative accounts is not allowed on vhess. Com so I think it's not safe but if you don't play against yourself don't increase or decrease your elo with the help of your other account, you can say that the other account is of your sibling or friend or someone that you know and he let's you play on it sometimes. So until you are not messing with your elo I think it's fine.
Is it breaking the rules if I enter my main and my alt accounts in the same team match?

In the first place making two alternative accounts is not allowed on vhess. Com so I think it's not safe but if you don't play against yourself don't increase or decrease your elo with the help of your other account, you can say that the other account is of your sibling or friend or someone that you know and he let's you play on it sometimes. So until you are not messing with your elo I think it's fine.
No, you are allowed an alt if you contact support, and I mean putting both accounts at the same side of the team match.

Making sure is this allowed or not?
That's against the rules.
https://support.chess.com/en/articles/8568381-can-i-have-multiple-accounts
You may NOTÂ
- Play in the same tournament with both accounts.

Making sure is this allowed or not?
That's against the rules.
https://support.chess.com/en/articles/8568381-can-i-have-multiple-accounts
You may NOTÂ
- Play in the same tournament with both accounts.
Does a team match count as a tournament?
Making sure is this allowed or not?