No. If Del Potro beats Tipsarevic and Federer in straight sets he'll make the semi-finals. If Del Potro beats both but drops a set in either he'll be 2-1 on matches and 5-3 in sets and assuming Ferrer beats Tipsarevic he'll also be 2-1 on matches and 5-3 in set and and will take the place over Del Potro based on him winning the match between the pair.
Nope. Ferrer is 2-3 in sets (2-1 vs Delpo, 0-2 vs Fed), if JMDP wins in 2 today he'll be 3-2 in sets. If he beats Fed 2-1, he goes 5-3, while Ferrer can go 4-3 max if he wins in two.
Not to mention that if JMDP wins in two today, a Tipsy win over Ferrer would make him qualify even if he lost in straights to Federer.