Go for it.
Brutes are supposed to be strong on their fortitude defense and have a bunch of hp while weak on AC, mobility, reflex, will, and accuracy. Improved toughness gives them +1/HD which can get to be significant, particularly for the more bestial opponents with lots of animal/magical beast HD for their CR.
At level 20, where this feat gives its maximum benefit, you only get 20 extra HP. Improved Toughness is best on casters or anyone else with tiny, D4 hit dice, and even then, casters have better option (Faerie Mysteries Initiate allows you to use Int instead of Con Mod for calculating HP for wizards, for example.)
For low level encounters toughness can make a significant difference. If you want to make your warrior 1 orcs into brute type combatants then toughness is not a bad feat choice.
At any other level, its usefulness drops off quickly.
HP and fortitude save boosting feats are appropriate to get part of the brute feel.
Good HP and fortitude save boosting feats are more appropriate.
I'd be interested in what you feel are better feats in 3.5 for getting the tough but relatively vulnerable part of the brute feel?
Steadfast Determination: Prerequisite Endurance. Allows you to use Con mod instead of Wis mod for will saves. Also prevents you from failing a fort save on a natural one.
The ones you listed before are only attack feats, and I'm not familiar with all of them and their prereqs.
Leap Attack requires 5 ranks in jump, and allows you to double the damage on a charge if wielding a two handed weapon. (The text says triple, but I'm fairly sure it was errata'd.)
Shock Trooper requires Improved Bull Rush, and allows you to assign your Power Attack penalties from a charge to your AC, among other things.
Combat Brute requires Improved Sunder, and allows you to take a penalty of -5 or more on an attack you make after charging and deal x3 damage if you wield a 2 handed weapon, among other things.
There's more you can add on to this, such as
Battle Jump and
Headlong Rush along with items such as a Valorous weapon (an enchantment that doubles the damage on a charge), and other ways of adding damage (Rhino's Hide armor from the PHB gives +2d6 on a charge)
Note: If you have two x2 charging damage feats (or items, or etc), the actual damage multiplier increases to x3, not x4. It just goes up a step. Likewise, if you had three x2 feats, it goes up to x4. (I think)
I postulate that this is a better use of feats.
Where is pounce a feat for example?
Pounce can be acquired through two Incarnum feats, Open Least Chakara and Sphinx Claws. Alternatively, have the Brute take one level in the Spirit Lion Totem Barbarian from Complete Champion for pounce as a class feature, or apply the +1 LA Feral template.
With Shock Trooper, Heedless Charge is about buffing your survivability while hitting for high damage, and the bull rush maneuvers are about positioning. I think that might be a skirmisher feat, since Brutes just sit there and get wailed on.
Skirmishers would be highly mobile, which to me evokes an image of spring attacking. Charging melee monsters that deal large damage on charges but don't have the mobility are not strikers to me.
I realize that Toughness is not a good feat, but it definitely belongs on the "brute feat list." Imagine toughness gave +50 hit points. Would you give it to every monster? No, you're not trying to optimize, you're trying to flavorize.
So why not use a feat that is both flavorful
and good?
Here's the issue with flavoring things without paying attention to the mechanics: you can spice up a monster all you want and make it seem like the deadliest thing on Oerth, but if it dies in one round after combat starts, then what's the point of your flavor? You have to have mechanics to back it up.
Take for example the CR 20 Tarresque. Flavored as this devastating monster... but you're effectively invulnerable to it if you can fly. Overland Flight is a spell that wizards get at level 9. It can be killed by a level 13 party that tries really hard, or by one level 20 caster that tries moderately hard.
What we have here is an example of the fluff being rather incongruitous with the crunch, and it turns the Tarresque from this massive threat to a joke.
Incidentally, I believe the Tarresque chose Toughness for all of its feats?