While it is true that Acts 4:12 states:
for there is no other name under heaven given to mankind by which we must be saved."
it is not true that the syllables must be uttered in a particular language. Unlike, say, the Qu'ran, no mainstream Christian denomination posits the necessity of a particularly holy language.
"Isa" is clearly the identification of the same individual that Christians call Jesus of Nazareth. It is a peculiarly Islamic name, and the Islamic understanding of who Jesus is differs, but it is the same individual. To the extent that one believes Isa died on a cross (something that a Qu'ranic interpretation would deny) and that Isa rose again (again, Qu'ranically contradindicated), then Salvation would come through Isa.
It is true that Muslims believe that Isa was a man, but they deny he actually died on the cross. They also deny he was God. But they do recognize him as a great prophet, teacher, and worker of miracles. As such, there is a basis on which to build.
Indeed, in the Muslim world. I have heard many reports of Central Asian missionaries retelling the stories of Muslims who have had dreams in which Isa has revealed himself to Muslims. Key to these dreams, however, is that he is who the Christians say he is - the Son of God who died on the cross and rose again.
The question, thus, is not, what will Jesus' name be in whatever target language, but rather, what attributes does he reveal of himself. Anecdotally, it is occurring (I wish I could find the movie I saw about this!). By leveraging what a person knows of Jesus, but correcting the errors, Isa makes the bridge to understanding.