Yes, that is true, but of course the comedians are our best source for short and colloquial phrases of this type.
Throughout basically all of Latin's history Terence in particular has been seen as a model for good Latin expression, so it should be noted that this use of "ut" is much less commonly found in his comedies than in the earlier comedies of Plautus, but there is at least one example of this use in the classical works of Horace and Livy.
It's in Lewis and Short, amidst dozens and dozens of other meanings, it's just one of those kinds of verbs, I think:
"In colloquial lang., to do, to fare, get on: quid agis? what are you doing? M. Tulli, quid agis? Cic. Cat. 1, 11: “Quid agis?” What's your business? Plaut. Stich. 2, 2, 9; also, How goes it with you? How are you?"
I don't see it neither.
1 to drive. to direct. to urge, induce. to pass, spend (a period of time). to emit, yield up, bring forth.
2 to do, perform (in general sense). to perform, practise (a specific act), to conduct, apply (procedure). to execute (an official act or document). to play the part of.
3 ) to act, conduct proceedings. to effect, contrive, design. to strive, venture. e to take legal action. to celebrate mass.
4 to promote. to contravene. to deal with. to deal with, treat of. to be in (a condition or place).
EDIT: See Michael783437's comment!
No, it's always a hard "g", they use "classical pronunciation".
In Ecclesiastical one, it's [d͡ʒ] before "e" and "i".
Marce is the vocative. You use it when you are addressing Marcus directly.
Quid agis, Marce? How are you, Marcus?
Marcus is the nominative. You use it when he is the subject of the sentence, being talked about to someone else.
Quid agit Marcus? How is Marcus?
Notice the verb conjugations as well. Agis is 2nd person singular. Agit is 3rd person singular.
I had essentially the same problem in a dictation. I heard "Quirarget Marcus", which obviously didn't make sense. I was quite surprised when I learned what the actual sentence is. Now with the knowledge what the sentence is, it makes sense. The audio quality just isn't good enough.
No, "Marcus" is not interchangeable with "Marce" any more than "I" is interchangeable with "me". "Marcus" is the nominative and "Marce" is the vocative.
Here is a plain-English overview of what the cases are and how they work:
Latin cases, in English
Adjectives must agree in gender, number, and case with the nouns they modify, but they have their own declensions. Sometimes you get lucky and the adjective just happens to follow the same declension as the noun, but that is not a guarantee.