Oh god, not this argument again. This thing lasted a good dozen pages last time.
According to the rules, UWB Radar implants qualify as vision, as they are susceptible to vision modifiers in the same manner as ultrasound. And according to SR4A, if you pay for it with essence, it is a part of you, and can be used to cast.
That being said, IT IS ENTIRELY UP TO THE DISCRETION OF YOUR GM WHETHER OR NOT THIS WORKS. Period. Full Stop. No further discussion. The rules as written are vague and using Radar for LOS is neither expressly allowed nor forbidden, so it is entirely up to your GM to decide whether or not it works.
Continuing discussion in this thread is simply the opinion of the posters, and not backed up by any rules. Unless one of them happens to be your GM, their word on the matter is no more useful than your own best guess.
If you really want to see the full extent of the argument for and against, just read one of the several old threads. I highly doubt anyone is going to say anything here that wasn't already said there.
http://forums.shadowrun4.com/index.php?topic=6834.0http://forums.shadowrun4.com/index.php?topic=6838.0and the tangentially related,
http://forums.shadowrun4.com/index.php?topic=6867.0