I've used Nicotine (gum), Ephedrine/Caffeine, just as also (I'm chewing on a 4mg piece of Nicorette as I speak, Ephedrine/Caffeine running course through my veins).
The combination can elevate blood pressure more so than normal, however (more than either used alone), but that is tolerance dependant.
If you're quite accustomed to Nicotine, then the E/C may have little (noticeable) impact (16 mgs of Nicotine per day, as of now does little to elevate the beating beyond that induced by E/C alone [1 Cigarette on average contains ~10 mgs of Nicotine, with only 1-3 mg(s) being absorbed. Per 4 mg piece of gum, around ~1.2 mgs is had at take------this is to give you a point of reference).
So, safe or not? That's not the proper question, as the answer is contextual. Take notice of your heart rate to ensure, as may happen, that it's not drumming at haste.