Can I cook 2 very different things at same time in the oven?
It is absolutely safe to do so...

For most foods, I would say that there is no reason not to.  If they are savory muffins like corn muffins to be served with the roast, I would not hesitate at all.

For sweet goods, with a high amount of butter or oil, there is some small risk of absorbing aromas.  I would generally segregating strongly aromatic foods for baked goods.  The foil should mitigate most of the possible transfer, but I wouldn't try it for the first time with guests.