There’s only risk of cancellation when you do a LtRt from a 5.1 mix (LoRo is just adding up, better skip the surrounds in general). In a 5.1 room channels are discrete, so cancellation couldn’t occur. But I wouldn’t just pan a single stereo recording to all channels, the result will sound flat, mono-ish.
A better way is using different moments in a single stereo recording and pan one moment to Ls/L and a second one to Rs/R, or make a diagonal pan of 2 stereo recordings. The result sounds lots more interesting than a simple spread. Just lookout for any repeating discrete sounds.
If you really have to use only 1 stereo track, use a surround reverb or upmix software to keep things somewhat discrete and prevent cancellation in the LtRt. Then add mono and stereo sources, just don’t diverge them all over..