Connecting antenna directly to RF module
The short answer is yes that could work provided you match the impedance. You essentially have a tree device connection (whether you use the transmission line 
or not) and all the impedances need to match (or be close).

$$Z_{antenna} \leftrightarrow Z_{connection} (via) \leftrightarrow Z_{TX/RX}$$

The longer answer is that there may be other engineering reasons to move the antenna away from the transmitter. Like @hcabral mentioned, there may be other practical things to consider when putting the antenna that close to the circuits e.g., electromagnetic interference (EMI), antenna loading, and unintentional radiation (maybe another circuit will couple to the antenna and produce unwanted radiation). Remember, with the antenna that close the whole board actually becomes the antenna. Another reason you may want a trace is for a balun. The antenna feed and TX/RX pin may not have the same impedance and therefore the trace may become a matching network.