I've used several different kinds of substrates for my plant tanks (aquarium gravel, "sand" bag gravel, pool filter sand, onyx sand, flourite, etc.), and they all work just fine as a plant substrate. However, the best results from my root feeding plants came from flourite and onyx sand, both which are made by Seachem. Substrate supplementing with things like root tabs is not needed, and its a good source of iron (among other things) for your plants. There are other plant substrates out there as well, and I've heard of people with good experiences with them as well. Of all the substrates that I've used/experiemented with, I like Seachem's substrates the most, and will continue to use them until I find something better.
Ordinary substrates will have no problems in supporting a planted tank, over time as the substrate matures, enough organic matter will settle into the substrate to provide a good nutrient source for plants that rely on root feeding. Initially, however, you may need to supplement the substrate with root tabs to give it a kick start. Other people mix in laterite with ordinary substrates to also give it a good kick start.
As with all substrates... you need to do some prep work. Put a light dusting of peat moss over the bottom of your tank. Then (if possible), take the mulm sucked out of a healthy tank, and spread that over the peat moss layer. After which, put your substrate on top of that. Doing so should help in the maturation process of your substrate.
On another note, Excel shouldn't be used alone for plant fertillizing. Excel is mainly a source of organic carbon for plants. The same results achieved with Excel can be duplicated through the use of CO2 injection. I advise against using Excel, as CO2 injection will be much cheaper in the long run.
HTH
-Richer