[Aquinasfan]

Is Mother Theresa really happier than Scott Peterson, or merely subjectively happier?

Did Scott Peterson ever aspired to be like Mother Theresa? I can write a huge and interesting essay here about how he feels and thinks...

Or you could answer the question. Is he really happier than Mother Theresa?

Does this invalidate the point, that a life of virtue will make one happier than a life of vice?

Only for those for whom virtue is a value.

So people who lead lives of vice can be objectively as happy as people who lead lives of virtue?

Members of the mafia are objectively as happy as the Sisters of Charity?

[Sapirit]

So people who lead lives of vice can be objectively as happy as people who lead lives of virtue?

remove the word "objectively". I can't answer any happiness-related question "objectively": everyone's idea of what's good is different, you can only evaluate happy/unhappy, right/wrong based on your set of beliefs.
Subjectively, yeah, S.Peterson could be feeling just as happy if not happier than Mother Theresa, at least until he got arrested. He operates on his level, Mother Theresa - on hers. If you're trying to say, that it's impossible to be happy without being moral, then again i will say everyone's idea of happiness is different.

[Modernman]

Members of the mafia are objectively as happy as the Sisters of Charity?

Depends. A mobster derives happiness from money, beating up his enemies and having sex with attractive women (among other things). If a mobster gets enough of these things, he will objectively be happier than the aformentioned Sister of Charity.