The short answer of it is No. But you need to make sure that you are abiding by their policy. One of the key items is ensuring people are directing that message towards you and not a wider audience. That's why HelloTweet will only auto reply to # keywords that include your @ name in the message. It's a higher probability, maybe 100%, that they are reaching out to you and your promotion.
If you tell someone to tweet @YourName #Keyword, then they're requesting you to send them more information, ultimately opting in. And they don't get another message until they ask for it.
This is quoted from Twitter's documentation on abuse:
The @reply and Mention functions are intended to make communication between users easier, and automating these processes in order to reach many users is considered an abuse of the feature. If you are automatically sending @reply messages or Mentions to many users, the recipients must request or approve this action in advance. For example, sending automated @replies based on keyword searches is not permitted.
Users should also have an easy way to opt-out of your service (in addition to the requirement that all users must opt-in before receiving the messages). We review blocks and reports of spam, so you’ll need to provide a clear way for users to opt-out from your messages.
For more information visit https://support.twitter.com/articles/76915#