Not really. An ambush is defined as a surprise attack on an unsuspecting person by someone lying in wait. The nuance may seem slight, but a person carrying out an ambush does so for the express purpose of attacking his victim or victims.
It is a fundamental tenant of the lawful use of force, deadly or otherwise, that it be used defensively, and, notwithstanding the verbiage of castle laws, only when the defender has reason to believe that it is necessary. The law may establish that the fact of an unlawful entry could provide a basis for that reason, but that basis may or may not prove adequate in the light of the totality of the evidence.
You do not want to go about doing anything that would indicate that your primary objective was to surprise and attack someone.
To stay in a safe position and to use deadly force when and if it becomes necessary to defend oneself or anyone else in the house from a forcible felony is not at all the same thing as planning to attack someone simply because he has entered the occupied structure unlawfully.
Probably, since it would probably be rather difficult for him to articulate a reasonable belief that his action had been immediately necessary to prevent a forcible felony, but the evidence against him would be weaker.
