No, certainly not. For Bulldoze to be worth a moveslot, it'd have to OHKO both of them. The best it'll do is 2HKO Magnezone, who moves first and beats you with HP Fire.
>0 Atk Ferrothorn Bulldoze vs. 248 HP / 0 Def Heatran: 156-188 (40.5 - 48.8%) -- 9.8% chance to 2HKO after Stealth Rock and Leftovers recovery
>0 Atk Ferrothorn Bulldoze vs. 0 HP / 4 Def Magnezone: 148-176 (52.6 - 62.6%) -- guaranteed 2HKO after Stealth Rock
Bulldoze won't do crap to Heatran, and your Ferrothorn will die afterwards. It'll 2HKO offensive Heatran, but Heatran can still OHKO Ferrothorn with whatever Fire move it's using. Against Magnezone, you fare slightly better, and can kill it in two hits if you can catch it on the switch-in at the cost of about half your HP. (Just make sure it's worth the risk they may be running Choice Specs, which kills Ferrothorn after Stealth Rock.) If you want to do any more damage, you'll need to run Attack investment. Sacrificing bulk just to power up such a mediocre move is not worth it. Knock Off has more overall utility, and so do other moves like Gyro Ball or Thunder Wave.
Ferrothorn isn't designed to deal with those Pokemon by itself, so don't try to make it. It's more effective to simply switch out to a Pokemon that can counter the Heatran or Magnezone. Pokemon like Air Balloon Heatran, Excadrill and Landorus-T can assist in countering these Pokemon. Defensive Landorus-T is actually a good idea if you really want to run Bulldoze, as it can use Stealth Rock. You can replace Stealth Rock on Ferrothorn with Bulldoze, though Spikes or Thunder Wave are still better options in my opinion.
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