Enzyme Inhibition by alpha-2 macroglobulin
Lets first see the proper definition of Suicide Inhibition as given by Wikipedia (emphasis mine):


  In biochemistry, suicide inhibition, also known as suicide inactivation or mechanism-based inhibition, is an irreversible form of enzyme inhibition that occurs when an enzyme binds $\alpha$ substrate analogue and forms an irreversible complex with it through a covalent bond during the "normal" catalysis reaction. The inhibitor binds to the active site where it is modified by the enzyme to produce a reactive group that reacts irreversibly to form a stable inhibitor-enzyme complex. This usually uses a prosthetic group or a coenzyme, forming electrophilic alpha and beta unsaturated carbonyl compounds and imines.


Now, lets see how $\alpha$-2-Macroglobulin works, again by Wikipedia (emphasis mine):


  $\alpha$M protease inhibitors inhibit by steric hindrance. The mechanism involves protease cleavage of the bait region, a segment of the $\alpha$M that is particularly susceptible to proteolytic cleavage, which initiates a conformational change such that the $\alpha$M collapses about the protease. In the resulting $\alpha$M-protease complex, the active site of the protease is sterically shielded, thus substantially decreasing access to protein substrates. Two additional events occur as a consequence of bait region cleavage, namely (i) the h-cysteinyl-g-glutamyl thiol ester becomes highly reactive and (ii) a major conformational change exposes a conserved COOH-terminal receptor binding domain (RBD). RBD exposure allows the $\alpha$M protease complex to bind to clearance receptors and be removed from circulation.


So, clearly, it is not suicide inhibition as:


$\alpha$M protease inhibitor does not form an irreversible complex with the protease, instead it uses steric hindrance to prevent protease from binding any substrate.
this inhibition does not occur during the "normal" catalysis reaction, it is after the protease has catalyzed a reaction that the inhibitor covers it up, more like the consequence of catalysis.
the inhibitor does not bind to protease active site, it covers the active site like a shield.



Putative mechanism of protease entrapment and inhibition by ECAM (Escherichia coli Alpha-2 Macroglobulin)

References:


Suicide Inhibition
$\alpha$-2 Macroglobulin
Structure of protease-cleaved Escherichia coli $\alpha$-2 macroglobulin reveals a putative mechanism of conformational activation for protease entrapment (PDF)