So let's take the research paper from at OP's post at face value. This is the the authors' table summarizing the antioxidants found in tobacco smoke:
Most of the claimed antioxidant effects are due to HCN and isoprene; the paper says
As shown in Table 4, HCN exhibited
the highest antioxidant activity (even more so than
total vapour phase) accounting for 92 % of total
inhibition. Isoprene, one of the major unsaturated
compounds, surprisingly had little effect even at a
concentration several times that found in smoke
vapour. A negative synergistic effect is seen where
HCN loses its efficiency when combined with isoprene
to give an activity similar to that of the total vapour
phase. This synergism probably accounts for the fact
that pure HCN by itself had a higher activity than
total vapour phase.
Obviously HCN is very toxic, causing tissue hypoxia which (at non-deadly levels) has quite a few manifestations including neurological, respiratory cardiovascular and thyroid defects. But if you want to get its full antioxidant "benefits", you're probably better off inhaling it apart from tobacco smoke... just from that analysis alone. I'm not seeing HCN vaping being very popular though.
What about isoprene? IARC says there's no human data for it but
Isoprene was tested for carcinogenicity in male mice and in male rats by inhalation
exposure in one-year studies. In mice, exposure to isoprene resulted in increased incidence
of benign and malignant tumours of the lung, liver and forestomach and of Harderian gland
adenomas. The study by inhalation in rats was inadequate for an assessment of carcinogenicity
As for the rest of the substances in that table, acrolein is an irritant. Carbon monoxide should be familiar to most. Probably the only thing there with a known therapeutic effect is nitric oxide, but even then, its effects are complex and dose-dependant. The poisonous effects of CN, CO, and NO share a common pathway in the inhibition of cytochrome c oxidase (COX), a mechanism in cell respiration, although the inhibition by NO is reversible.
So even if these components can function as antioxidants, this is basically a smoke and mirror exercise by associating a list of substances mostly with no health benefit with a word that most people think as good because the usual, dietary antioxidants talked about in the press are vitamins (C, E) and their precursors like beta-carotene etc. And even for those, the story is not always "more is better".
Also according to some recent research, isoprene ranks first among the contributors to a theoretical cancer hazard index in tobacco smoke (using animal model, I think) while acrolein and hydrogen cyanide overwhelmingly account for the non-cancer health hazards.
Amusingly, this last paper is also from a German consultant for tobacco companies. The venue is a bit more respectable though. The data in these two graphs is entirely from the Chinese paper cited (I've checked it), whose authors' declare no conflict of interest... even though the all seem to work for either a US Big Tobacco company or an obscure institute belonging to CNTC. So while the exact quotients here aren't that certain (not just because of the source, but also because of the methodological limitations), it's interesting to see how the same substances now fly under a different flag.