Torchwood is a guilty pleasure for me apart from the third series which is genuinely excellent and the fourth series which is genuinely awful.
It's generally a deeply stupid show that desperately wants to be Buffy or Angel. Owen was a really cool character though.
To answer the OP's question, you will understand TW just fine without seeing Who. Although a brief Wikipedia research of Jack Harkness's 5 episode stint in Who before TW started would be recommended.