This is impossible with Bitcoin. Bitcoins can only be created via mining, Bitcoin mining is a proof-of-work crypto currency. Crypto's typically use proof-of-work or proof-of-stake in order to have value.
Tether, on the other hand, seems to have no proof-of-work or proof-of-stake at all and just claims to have a 1:1 ratio of their currency to dollars. Seems there is some skepticism around this claim of a 1:1 ratio.
If Tether, was found out to be a fraud I think it would have minimal impact on real Crypto currencies that use proof-of-work or proof-of-stake. The only negative impact would be the people that exchanged a real Crytpo for Tether might be burned and decided not to use/accept Crypto at all, which could impact the larger Crypto market a bit, but IMO I don't think it would shake it too badly, unless of course the main stream media took the story and click baited it with crappy headlines and poorly written articles that would falsely come to the conclusion that such a artificial pump is possible with real Crypto.