What is the meaning of "a5ultexx" in terms of phone models?
a500fu or a5ultexx are codenames, but not necessarily ones given by the manufacturer. ROM maintainers will determine a suitable codename representative of the device in the bringup process, and that codename can change during the device's life cycle (in another answer of mine, I described a similar change to another device).
For recent Samsung devices there's an undocumented (AFAIK) pattern in the codenames. Take your device for example:

a5ultexx = SM-A500FU

a5 is obviously Galaxy A5
u for sub-variant, the &quot;U&quot; in &quot;A500FU&quot; - this part is rarely seen
lte for LTE variants, versus wifi for WiFi-only tablets, or 3g for 3G variants.
xx for general region/carrier, in this case, for international devices, the &quot;F&quot; in &quot;A500FU&quot;.


As you can see the 2 expressions point to the same device, so yours is compatible.