I have seen many apple trees planted incorrectly. It is extremely important to have the apple tree at the correct depth. The depth must be BELOW the graft union. All trees today will be grafted. Whether it is a semi dwarf or a dwarf tree it will be grafted and will need to be planted correctly.
Planting the apple tree into a landscape garden is a common sense plan. However, remember the tree will need a stake/pole and it will need to be planted to allow mulching to build up a little without covering the graft union.
What if my tree is planted too deep?
The issue is called Scion Rooting. This means the variety which is not dwarfed sends roots down. These roots will take over and the restriction of the dwarf rootstock will loose effect. Normally by the age of 6-8 the tree will have a truck twice the size of the other trees planted correctly.
This excess growth will allow the tree to grow 20+ ft tall and be out of control. Pruning will be difficult and nearly impossible to manage. The tree will be less productive as it is growing much too fast and to keep it within its space the grower must prune it hard.
The graft union is a weak point in the tree. Heavy winds or crop load will break the tree off at this union. A post or trellis system to hold the tree stationary is necessary.