Did Shakespeare use dactyls or dactilic meter?

It is an interesting fact about the iambus that in ancient Greek verse, the iambic unit is not short-long (two syllables) but short-long-short-long (four syllables). The first syllable could be long as well as short. And the long second syllable could be ‘resolved’ into two short syllables! So you could legally have an iambus like this

long-short-short-short-long

So there could be something like a dactyl. It was a kind of syncopation. It happens more in later Greek tragedy than i. archaic verse, and most of all (not surprisingly) in comedy, where you could get something like:

ti-ti-ti-ti-ti-tum-ti-tum ...S a single iambus.

Syncopation involves playing one rhythm against another. Any poetic rhythm can be syncopated for effect. So when Macbeth heard of Lady Macbeth’s death he. laments

Tomorrow and tomorrow and tomorrow

Creeps in this petty pace from day to day

And all our yesterdays have lighted fools

the way to dusty death. Out brief candle.

you will notice how he makes the first line drag because of the clash between the iambic movement in your head and the rhythm you hear. Any word that comes out long when it should be short gets more attention. “Creeps” immediately stalls the line making it creep along. You can say that that opening word is a ‘spondée ’ (tum tum) rather than an iambus. But that would miss the point. Better to say it is spondaic.

Your passage is the same.

to bé or nót to bé thát is the quéstion.

Here, by reversing the stress the unexpected weight on that worth swells it’s importance. Even more does the “Out (stressed exactly where it should be unstressed and the first of three stressed monosyllables. That sentence could be read as a spondée trochee (stressed stressed / unstressed).

Of course, that is not how Shakespeare thought about it, any more than you or I think about grammatical usage most of the time we write. But it is reasonable to point out that “that is the” is dactylic in its movement. In that sense you are right to observe dactylic moments in this iambic verse.