As the tweets contain both SumAll-related hash tags and Links to SumAll, this is definitely marketing that should be opt-in, not opt-out. Unless the user of you

As the tweets contain both SumAll-related hash tags and Links to SumAll, this is definitely marketing that should be opt-in, not opt-out. Unless the user of your service is explicitly made aware of these automated tweets in clear terms when they sign up, this is a bit shady and dishonest to say the least.