You can use SAM to idle hours, it would be easier for you.

You can't get cards from games you don't own.

引用自 RauthRudolf：

My question was if its safe to use IM with CS:GO while NOT playing the actual game, but playing something else.

Yes.

Don't play on VAC servers while using IM and you're 100% safe.

Free to play games drop game cards based on your in-game purchasing. For every $9 USD spent (approximate) since the start of the Steam Trading Card Beta, you will earn one card drop. This card will drop at some point as you play. If you have made in-game purchases in Dota 2 or Team Fortress 2 prior to the Steam Trading Card Beta, or if you owned Team Fortress 2 prior to the Free to Play update, you will have 4 or 5 additional card drops available.

It's a FAQ about trading cards.
Buy more games - idle more cards, easy as pie.

http://psteamcommunity.yuanyoumao.com/tradingcards/faq

Don't play on VAC secured servers while use IM dude :)

Buy more games

What about free to play games like Team Fortress 2 or Dota 2?

Free to play games drop game cards based on your in-game purchasing. For every $9 USD spent (approximate) since the start of the Steam Trading Card Beta, you will earn one card drop. This card will drop at some point as you play. If you have made in-game purchases in Dota 2 or Team Fortress 2 prior to the Steam Trading Card Beta, or if you owned Team Fortress 2 prior to the Free to Play update, you will have 4 or 5 additional card drops available.

http://psteamcommunity.yuanyoumao.com/tradingcards/faq