Another way to say this question would be "Ut valet Marcus?" in that case it would mean "How does Marcus' health serve?"
"Ut" can indeed mean "how", and you find "ut valet", "ut vales", "ut valetur", etc. in the authors.
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.
That is the literal meaning, and that answer was accepted 13 September 2019.
See the notes on the same construction with Livia. This isn't what it means, even idiomatically.
Here is a link with some discussion:
And a lengthy dictionary entry:
Sounds totally different. Weird. It sounds 'Mag amet Marcus' or something. Maybe there's some problem in system.