No, it is not possible to swap USDT ERC to USDT Tezos without using a centralized exchange (CEX). Tether.io is a platform that allows users to trade between different stablecoins, but it does not support the swapping of USDT ERC to USDT Tezos. In order to do so, you would need to use a CEX that supports both ERC20 and Tezos tokens. Some popular CEXs that offer this service are Binance, Coinbase, and Kraken.