Veterans may include 3 special weapons, as well as a veteran weapons team with heavy weapon... so in that regard your fine.

Mech guard lists are very strong right now, mostly due to the Chimera. I'd include the heavy stubber for the 10 points, for 65 points your chimera has 9 shots stationary or 6 on the move since the stubber is defensive. I personally think you'd be better off with all chimera, though the Valks are very cool looking models, though in my opinion not as effective as the chimera. If you run all chimera the veterans to me are a points sink, they don't do anything that an infantry platoon won't. With the 5 fire points on the chimera your command squads should be all flamer or melta for the "drive by". Though there is something to be said about that extra balistic skill.

I'd consider dropping out the Demolishers for Basilisks, they'll get a cover save while being able to fire over the Chimeras(which really can sit still for the first few turns). Camo netting is useful, though at 30pts expensive. You have lots of melta so I don't know if you need more AP2 or anti tank that the demolisher provides.

Having recently played against a chimera heavy guard list lately I can say that they are extremely difficult to deal with. I was fortunate that I'm mostly in drop pods, so could get right up to them early, though I still soundly lost the primary.

For those of you who think gun lines are dead try playing against 13 chimeras and 2 basilisks in 1850, something like 107 shots per turn at the 36" line. Add to that the fact that 10 of those squads are troops and it's a very hard nut to crack. This list here seems very solid in 1500 points. I personally think that this style of list will be very popular in the future.

The choice of veterans over a platoon is more about the number of Chimeras. If using Valks, vets are likely your best bet, with more special weapons and a higher balistic skill they'll be able to disembark and stand a very good chance of dealing with thier target. If you plan to stick with 3 valks/vendettas the veterans are a good choice.

I do like the 3 lascannons on the vendetta, have yet to see one played but with mobility it should be able to get into side arcs of fire.

Keep in mind that the basilisk can fire directly, it's minimum range of 36" is only for its "indirect" fire option. It should be able to see over the chimeras at most targets, and the 2d6 roll for the armour pen means it can stand a good chance at heavier armour. With the points you save on just 1 basilisk instead of a demolisher you could get your stubbers, and whatever other upgrades you wanted.

And yeah, the "infantry gun line" is outdated, but lists like this allow you to stand and shoot the hell out of your enemy. Once you pass the 100 shots per turn mark you stand a good chance of either wiping out your opponent or being able to move up and take objectives in the last few turns with little resisitance.

Page 58, Ordnance Barrage Weapons