I think you'll find vapers who exercise and even a few very aerobic exercisers. I will say my lung capacity improved a great deal (I yoga) but I was a smoker, not a chewer, so your situation may be different. If you are worried, you could go get lung capacity tests (like a spirometer, you can also get a cheap, at home version, I think, we had one for my kid due to asthma) and then again in about a year (here's the thing, my doc told me that lung changes take place fairly slowly he did not give me the test when I asked, although he did say my lungs looked and sounded better.
So you'd be taking a risk to be honest, how big of risk I have no idea. If you want to continue harm reduction you could switch to Swedish snus, (you can find it in the US under "General Snus" and it is supposedly much safer than chewing tobacco and arguably less gross.
Good luck in your decision, it's really something you'd have to decide for yourself, as there are no definitive "does vaping impair your lung function compared to just not vaping.) I mean a decent case can be made that vaping is safe but how safe, over the long term, is just something there aren't clear answers to, really.
Good luck,
Anna