No you won't set the OPT on fire, but repeated trips into saturation might make your output tubes mad (red faced kinda mad).
I used an Antek power toroid as an OPT in a guitar amp back in the Hundred Buck Amp Challenge. The idea was to build a guitar amp for minimum $$$, but no more than $100 total parts cost.
I made a real cheap amp, less than $50. It used $4 worth of tubes and a $5 line matching transformer for the OPT. It made 4 watts, screamed real good and I still play it.
I made a second amp that cost about $99.99 to see what I could do for $100. It used an Antek toroid for the OPT. I think it was a 50VA unit, but I'm not totally sure. It was a 9 volt unit since I needed about 3 K ohms. The amp made 20 watts of clean power, but the lowest note on a guitar is 82Hz. The OPT was not the limiting factor, the tubes and the B+ voltage were.
