@dfnceto use smoke to protect yourself after shooting is perfectly fine, even when your smoke affects also other players. It can be sometimes annoying for other players, yesterday on SPEC OPS chap.4 I was in a T15 and right at the beginning after i did spot the very first enemies you find someone, i guess an MBT used the smoke after firing, preventing me to see the bots that was still blind shooting at me, so I took some damage that probably I would not have taken and the smoke did not had a real reason as blinded us all and the MBT had armor to deal with the bots. It can be annoying, but is fine, a player has the right to protect himself.
Also using your smoke to protect a squishy, or also a low health MBT that is taking too much shots, is perfectly fine.
But I was commenting about a different thing, to pop out the smoke in a way that prevents a person that is also spotting the target while you continue to spot the enemy, the image you posted is very clear about it. Here the reason to pop out the smoke is not your own protection as you are waiting to reload or protect a team mate at risk, is to affect negatively the playing of an other player, as not only you prevent him from maybe spotting further tanks (he can have better view range then you, maybe for the commander or the retros he uses), but to be surrounded by smoke for no reason is annoying in itself and can make his action less precise, ie for him is more difficult to judge if a weak spot of the enemy is or not is behind some hard cover a he sees only the red silhouette of the enemy in a white background.
About the fact that the support fire tanks can designate or track it is true, but also an MBT that is on the front line can track and so get the assist damage for the damage done by the tanks "on the hill" and if he can not designate has plenty of situations in PvE where he can push and spot while the good camo squishy tanks can not. In the match results I see a lot of MBT drivers getting a lot of spotting damage, often even not very good players judging their overall result, while to see a camo based tank getting a lot of spotting damage also happens, but imo less frequently, you actually need skill to do it and even with skill if the MBTs push too hard in some missions most of what you would have spotted has been already seen by them.
So I don't think that a front line tank, typically an MBT, but it can also be some Ramka or T15, has perform a tactic that can annoy other players only to farm more assist damage as there is not a bias in how the different classes can get assist damage and if there is some are the MBTs at an advantage given average the level of skill of the PvE player base and based on the average of the results i see. If a MBT driver wants more assist damage to push harder and spot more is all he needs to do, to annoy other people popping out smoke in front of them, but in a way that prevents only them to see and only for the purpose of preventing them to see is imho not the way to go.
And even if I am not sure if reporting such behavior has consequences, as you don't get a real feedback when you report someone, I would probably report who does so, like I report those that ram other tanks out a position to take it themselves, maybe causing the death of that tank that is pushed out of cover in plain sight of the enemies and every not fair behavior. Even driving in front of an ally closing his line of fire is not allowed by the game rules, and those things are even worst imo.