You can do, but as I say, it could potentially cause your PC to become unstable.
Personally, I always try and keep the same mix of modules, using the same size, speed and manufacturer.
I've had a problem in the past where I bought two sticks. Then I bought another two a few months later, and although they were exactly the same, and from the same manufacturer and should have matched up, they wouldn't all run together.
Separately they were all fine.
In the end I RMA'd the lot and bought 4 in one go.
Unfortunately the only way you will find out is by buying them and giving it a try.
If possible, check to see if the Crucial and the Rendition modules are rated at the same voltage, and same latency timings.
If so, they are more likely to 'match'