MailChimp with wp plugins.

I have developed few free plugins for wp in that i have integrated welcome screen and also a mailchimp subscribe form. from where user can subscribe to your mailing list.

is that allowed in envato ?
can i submit plugins with welcome screen + mailchimp subscribe form ?

I don’t see why not? Just make sure it’s as easy as possible - and as quick as possible - for the user to install and use your plugin. Only make the form/welcome screen show in the wp-admin.