You can co-opt the term [evangelical] and redefine it, but it should be used as popular culture and historical Christianity use it (reserved for us, not every false religion under the sun). It is more than any false set of beliefs or those who share some sort of belief system. It is the Good News of Christ, not the bad news of Buddhism. Evangelical Muslim would also sound like an oxymoron and they have the integrity to not blur the distinction or create confusion. Christian Buddhist may be possible in a Buddhist's mind, but it is not a biblical option for a true Christian (Eph. 1:3; 2 Peter 1:3; Jn. 14:6; Acts 4:12; Rom. 10:9-10).
Religions, including Buddhism, have behavioral truths in common with Christianity. Christianity (biblical, historical, orthodox) alone has redemptive truth leading to eternal life (Jn. 3:16; Jn. 14:6; Acts 4:12; Rom. 1:16; I Jn. 5:11-13).
Buddhism is bankrupt and false since Buddha is dead, was not Deity, did not rise from the dead, denies the existence of a personal God, denies reality of sin and need for a sinless Savior, etc. It may be a world religion or popular fad for some, but it is not revelatory truth (in fact it is demonically energized leading to deception of millions).