This is a nice idea for several reasons.
First: putting rails on tanks at the cost of armor is a high risk support role for the tanker. What may have been able to protect them from four or five HEAT rounds from an enemy MBT now can only protect them against two to four. But, throw two infantry men on each side, and you're able to drive them into battle for a variety of purposes like supporting the vanguard force or for spec ops runs. Give the infantrymen access to their weapons and you've got slightly more firepower in exchange for the armor.
Second: regarding aircraft, sure the galaxy is the greatest troop transport/gunship available, but keep in mind that while the galaxy is the troop transport of choice, it is the riskiest vehicle to be in. Everyone who's played anti-air tell me you haven't stopped shooting at those annoying mossies and reavers and started unleashing hell on an incoming galaxy, regardless of your health and danger. This also opens up the option for relatively stealthy drops. Two to four infantrymen strapped onto the sides of a mosquito flying low and bringing them just close enough to the front to cause a little mayhem. Basically instead of flying in a bunch of C-130's, you'll be flying in a few Huey's packing a strike team.
And third: Come on, we've all seen war movies with a bunch of soldiers sitting on the side of tanks on their way to the battlefront. Not all soldiers in PS2 will have the option of flying in on a gal, or purchasing their own vehicle, which means that they'll have a good five or ten minute run to the battlefront. I would sure be kinder to tankers and pilots willing to play taxi.
Just my opinions, of course. I like it
