I'd say that's a bit borderline choice.
I don't completely agree with those who say that the second example suggests triplets: while implicit triplets are considered normal writing practice, they rarely exist since the beginning of the piece (or the section), and at least the first group(s) or bar explicitly write it.
Yes, from a first glance they can look like triplets, but after seeing the first full bar it's clear that they are not (also, the "Tempo di Tango" is an important hint).
Also, when writing, it's important to consider the "target audience" of the score (as in the reader, not the listener). A musician accustomed to that repertoire would never have a doubt about that.
Then, the example referenced by Carl Witthoft is an interesting one to consider.
In that case the rhythm is clearly played for both the melody and the accompaniment, meaning that the actual metre is not 3+3+3 but 2+2+2+3.
This tango style is not that different, though: the whole rhythm section plays 3+3+2, and the melody usually follows a very similar pattern.
Considering this, using the same writing pattern would be coherent (and correct).
The problem comes when any rhythm stops following that pattern.
Let's take a basic rhythm:
Grouping should always follow the meter structure, so it means that then you should theoretically do this:
That is clearly terrible. Any musician would want to throw something at you for that.
The fact is: for meters clearly based on 4/4 (no matter their "groove"), it's usually unnecessary to use those subdivisions. They usually make sense only for complex pieces in which there are lots of meter changes with additive rhythms, so when it comes an actual 3+3+2 you really should write it in that way (even with the difficult writing above).
Then again, it depends on who's reading. For a rhythm section (bass, percussions, etc), it totally makes sense to have a 3+3+2 grouping. As a percussionist, I'd prefer it for this kind of music, since it really makes it clear what is the feeling I've to transmit in my playing, especially if no multiple rests are used: since most percussion instruments don't have a real sustain, having lots of rests is just distracting.
A typical and often preferred writing would be like this (note the staccato dots):