Does an heavy propeller aircraft (CS-25) have the Blu Line (Vyse) displayed on ASI? Does a propeller aircraft that is categorized as CS-25 (EASA Regulation) have the Blue Line (Vyse) mandatory displyed on ASI? 
I know that would be the case for lighter aircraft (Less than 19000 lbs /8600kg), but my question is related for heavy aircraft (Dash8 example).
No, larger aircraft typically don't have such speeds shown on the ASI because they vary significantly with weight. See also Why don&#39;t Transport Category aircraft have a listed Vy?.

For the Dash-8 Q400 for example, the $V_{\text{y}_\text{SE}}$ speed is called $V_\text{CLIMB}$:


  VCLIMB – Single-engine best rate-of-climb speed.


The following table shows the values for $V_\text{CLIMB}$ as a function of weight:

+-----------+--------+
|  Weight   | VCLIMB |
+-----------+--------+
| 18.000 kg | 130 kt |
| 20.000 kg | 131 kt |
| 22.000 kg | 137 kt |
| 24.000 kg | 143 kt |
| 26.000 kg | 148 kt |
| 28.000 kg | 154 kt |
| 29.000 kg | 158 kt |
+-----------+--------+


As you can see, the values vary too much to show a single blue line on the ASI.

This does not mean that the speed cannot be displayed at all. The Dash-8 Q400 has a Primary Flight Display (PFD) and can show up to 5 speed markers on the speed tape ($V_1$, $V_\text{R}$, $V_2$ and two more called #1 and #2, typically used for $V_\text{FRI}$ and $V_\text{CLIMB}$ respectively during takeoff and initial climb).


(Dash-8 Q400 FCOM - Indicating and Recording Systems)

The resulting markers on the PFD look like this:


(Dash-8 Q400 FCOM - Indicating and Recording Systems)

The electronic standby instrument does not show these markers.