No and this was also asked and answered in many other threads here already before
Addons cannot get any position of any unit except if you are grouped.
And they cannot draw any icon above others without having the exact positions + drawing icons and textures or using beams inside dungeons does neither work.
You can only exchange the textures of already given group members above their heads, that's all.
Sending data between non grouped players is not possible except if they would be in the same guild via guild messages but changing them too often (like more than once every 2 seconds) will most likely kick you from the server for message spam + the messages are also already used for many addons and thus the text is already fully used. Nevertheless it would be no good idea to send data via thase texts as it is too slow for positions etc.