Given that the Empire is based on the Holy Roman Empire, we may take the lead from history:
1. As SOF says, very much so. Merchants & bankers like the Fugger and Turn & Taxis even rose to become high nobility. Of course, the old Nobility continued to regard them as upstarts for a long time. The quick rise of Jakob Fugger caused a bit of a stir. In an extraordinary and murky deal, he had bought in 1507 the Reichsgrafschaft Kirchberg, while still being a commoner, and the local nobility refused to recognise him. The problem only got sorted more or less in 1514, when he was elevated to Reichsgraf.
2. These merchants and their successors continued their mercantile practices after their elevation. Indeed, this proved to be the basis for their continued rise.
3. Already in the Middle Ages, a coat of arms was not limited to nobility. Upon ennoblement, a commoner could keep his coat of arms (if he already had one). Usually, the coat of arms was altered somewhat, for instance, to incorporate the coat of arms attached to a fiefdom he might have gotten.
4. Within the HRE, ennoblement was in principle the prerogative of the emperor. The King of Bohemia, being a king, had also that right within his territory. The first example of a commoner to be ennobled was in 1360, when a Wicker Frosch received his patent of nobility from Emperor Karl IV.
There were, however, some others that had gained the privilege (for certain titles):
- The Archduke of Austria
- The Duke of Lorraine
- The Elector of Bavaria
- The Elector of the Palatinate
- The Archbishops of Salzburg
- The bishops of Metz and Toul
So, it would not be surprising if at least some Elector Counts would have the same privilege (but limited to certain titles).