Heartwarder question

[Beldar]

Does anyone know if Heartwarder works for warlocks? I think I could make a chaotic good warlock (never certain of the alignment restrictions). The description of Heartwarder spellcasting states:

Spellcasting: At each heartwarder level, the character gains new spells per day (and spells known, if applicable) as if she had also gained a level in a divine spellcasting, arcane spellcasting, or invocation-based class she belonged to before adding the prestige class. If a character had more than one spellcasting class before becoming a heartwarder, she must decide which class she increases when she gains a level.

I guess my question could be rephrased: Is warlock an invocation based class? I believe the answer is yes. Also what does 3rd level spell casting mean for a warlock? Greater invocations?

I bet you can guess what kind of character I am thinking about building.

[triskavanski]

A warlock with insanely high DCs?

[Kaedrin]

You gain new invocations and your eldritch blast improves as if gaining a level in warlock. Your warlock specials (fiendish resilience, etc) do not improve.

It's a low bab/hd choice for warlocks but it is available.

Greater Invocations are required if I remember right.