Tether is not a individual organisation but comprises of Tether Holdings Limited, BFXNA Inc., iFinex Inc. They have shareholders from these individual organisation. The major share are being held by BFXNA ( around 36% ).

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If its considered to be exchanged 1:1 to USD (according to coinmarketcap), will it can be in danger of being seized by FBI or government?

That is the major misconception among traders that USDT: USD is always 1:1 but Trade and market does not follow this even the data does not agree to this.
We don't follow coinmarketcap data nor any serious organisation and banks follow it, though for you information if you look in the history of Tether data then you can easily find that sometime back 1 USDT = 1.21 USD [ This was ATH ] and again it was low like 1 USDT = 0.6 USDT [ This was ATL ]. ( Source )
There is a lot of analysis that i have in mind but that's all trading games. Hope you understand it better now, not always USDT can cap your loss.

Brad
Knowledge based support
Straddle.fund
Geneva Branch