Balrog and servants of Sauron

[SamwiseGamgee]

As Sauron seemingly had no power over the Balrog for this creature is too old and too powerful for that

This isn't necessarily true. Although both Sauron and the balrog are Maiar, Sauron is described as 'the greatest' (Valaquenta Of The Enemies.)
Also, Gothmog, High-Captain of the Balrogs was below Sauron under Morgoth, so there is no reason to suppose that Sauron could not command a balrog.
In Appendix A III, it says:

The Dwarves delved deep...Thus they roused from sleep... a Balrog of Morgoth.

But also, in the footnotes:

it may well be it had already been awakened by the malice of Sauron.

So, it seems like there's no conclusive proof in the text- this is perhaps a bit of a 'do balrogs have wings?' or 'is Gothmog in RotK a Nazgul?', but it's interesting to speculate nonetheless.
I think that if Sauron could awake the Balrog conciously then he would. He could command it, and even if the fellowship had not passed through Moria, Durin's Bane would have been a valuable ally. And if it was not in fact awoken by Sauron we know that he would have been aware of it. In Appendix B the Balrog is said to have reappeared in the year 1980 of the Third Age. It is said that: 'Sauron begins to people Moria with his creatures' in the year 2480 of the Third Age. So we can speculate that even if Sauron did not intentionally awaken the Balrog, he certainly began an attempted 'recruitment' 50 years later.