Lostspark:
Great question!
My response as a Lubavitcher:
Since the “founding” of the “state” in 1948, Lubavitch has become less VOCAL about their opposition to Zionism, the reasons for which are discussed in the sefer mentioned by sechel, and other places.
(This change was already brought about by the Rebbe Rayatz. As a matter of fact, the Rebbe was much more vocal about anti-zionism than his father-in-law was in his later years).
Due to this, unfortunately, there are Lubavitchers nowadays who are ignorant of our shita on zionism and may confuse strongly supporting Eretz Yisroel with promoting zionist symbols r”l.
The Rebbe was adamantly opposed to the hanging of the flag, singing hatikva, celebrating yom haatzmaut, and even referring to Eretz Yisroel as “state of Israel.”
The Rebbe stripped his נשיאות from Tomchei Tmimim (the central Chabad yeshiva) in 5715 when they allowed a balebos to sing “הניגון הידוע” (the Rebbe wouldn’t even refer to it by name) at a dinner.
On a separate occasion, the Rebbe wrote that singing this can interrupt Hashem’s brochos to the institution.
The Rebbe railed against the concept of אתחלתא דגאולה in no uncertain terms, even saying that this idea has brought much darkness and hardships to klal Yisroel (I won’t get into specifics due to the public nature of this site).
At the Lag B’omer parades, children would march with American flag and Tzivos Hashem flag, but the zionist flag was not allowed.
B”H, most Lubavitchers and shluchim know this info, and keep a proper balance between supporting the Yidden in Eretz Yisroel while rejecting the zionist ideology and symbols.
Unfortunately, there are indeed some who are either uneducated on the subject, or were unable to withstand the נסיון of appealing to the wider Jewish public and have allowed such symbols and ideologies to infiltrate their Chabad Houses, etc.
These are B”H not many (though they may be vocal), and I and others have done our best to reach out to these people and influence them to correct their ways.
It’s also important to note that some may call themselves Lubavitchers while being totally rejected by Lubavitch. Figures such as Shmuley Boteach who has been banned by Chabad rabbis and doesn’t represent us whatsoever.
In conclusion: No, Chabad is not zionist. Our IDEOLOGY has not changed one iota from the times of the Rebbe Rashab (as opposed to the manner of vocalizing our ideology).
P.S. Joining IDF is a completely separate issue that has nothing to do with zionism. However, I would still venture to say that it’s still the same type of bochurim that you described (though I wouldn’t describe them that way) who join, because for the most part, the way for yeshiva bochurim to protect Eretz Yisroel is solely through limmud hatorah.
Re magen davids: While there are issues with the symbol, it’s in no way comparable to the zionist flag.