I think RAW, the Ambuscading Spell feat would not apply to spells such as Dimensional Anchor or the Combat Maneuver effect of Telekinesis.
"During a surprise round, your opponents that have not yet acted take a –2 penalty on saving throws against spells you cast. Creatures that have already acted take a –1 penalty during the surprise round."
But RAI, the feat's description seems to suggest otherwise: "Your spells are particularly effective against those caught unawares."
Any evidence out there to support the latter? Other than having a cooperative GM?
Dimensional Anchor says "Saving Throw none". So Ambuscading Spell does nothing, as there is no saving throw to affect.