Using multiple accounts in the forum is allowed, but I don't think it's really healthy for the forum.
Another thing is that more than 70% of the bounty and signature campaigns that I have come across don't allow participants to participate with more than one account. Because it will look like spamming for you to be promoting the same project using two different accounts.

But I don't think there is anything wrong if you have one account and an alt and are using them for separate campaigns and not joining the same campaign using those accounts all at once.

You can promote different projects with your different accounts, one for each other, if you are good enough and have time to actually handle those accounts. Don't make a bunch of spam posts or copy and paste on social media just to meet your weekly requirements.