Like the others have said, the main problem here is that not only are instincts and emotions not opposed, I'd go so far as to say emotions are instincts or rather, emotions are how sentient beings experience instincts. Because of this it's quite difficult to envision of a race that acts on instinct and is sentient but doesn't experience emotion.
It would make more sense to have them experience and/or process the emotions differently or experience different emotions. I would advise you to collect all of their instinctive reactions and envision for yourself how it would feel for them to experience these reactions. That's their base emotions. If you don't want them to "feel" emotional in the way humans do, you might say that these reactions happen subconsciously and the decisions based upon them are mostly just accepted as fact by their consciousness. For example, while a human being might be delighted by something delicious and improve their overall mood, the reaction of your reptilians may then play out in their conscious mind as "This is good food. I should eat more of it."
Evolution plays an important role here just as it does for emotions and aesthetics in humans. Humans like art because it makes them feel something, but that emotional reaction is also an instinct and it is one that evolved. It's likely that works of art come from an appreciation of good craftsmanship which is a useful trait. Furthermore, the ability to produce purely artistic pieces is also a sign of abundant resources, again a useful indicator of success. From there, it pretty much just progresses into symbolic abstraction of concepts.
Religion too is a much more instinctive than rational endeavour. Many scholars have surmised that humans may be evolutionarily predisposed to believe in gods or spirits. Children tend to be natural mind-matter dualists and they also exhibit the trait of a teleological world view - they believe that things are there for a purpose. The hypothesis goes that humans as inherently tool-using animals (a strongly defining trait maybe only second to language) tend to instinctively view things in terms of their use and usefulness and, as they "make" things will also instinctively assume that everything is made by someone - and for a purpose. From there a bigger, more powerful anthropomorphic being is extrapolated (it creates like us, only bigger - it must be like us, only bigger!).
Another factor is that humans have an overactive centre of pattern recognition, which means that we'll tend to see patterns and especially agency in things that may be coincidental. This is a basis for beliefs in fate as well as spirits and animism.
So to come back to your question: it is entirely possible and even quite likely for a largely instinct-driven race to have art and religion, only that their form and expression may be somewhat different. For specifics you really need to think about what instincts these reptilians have, why they have them (i.e. how they evolved) and then extrapolate from there how this would lead to religious assumptions and aesthetic expression and appreciation.