The oxidation of hydrazones produce a diazo compound: orgsyn.org - DIAZOPROPANE.
An intermediate in the Bamford-Stevens reaction is a diazo moiety.
Most aliphatic diazo compounds are exceptionally unstable and they generally decompose as soon as they are formed, giving alkyl carbenium ions. Note that some compounds are fairly (usefully, but not indefinitely) stable in solution in an inert solvent, like diazomethane in diethyl ether solution. The carbenium ions formed on decomposition quickly rearrange and/or react with whatever molecule/ion is nearby (solvent, dissolved ions, etc.) to produce any number of products. Alkenes can be formed, but it depends greatly on reaction conditions.
After the diazo compound decomposes with loss of a nitrogen molecule, the free carbenium ion can expel a proton and become an alkene. It could also react with water to form an alcohol. If large amounts of acid are present, it can combine with the anion to form an ester, e.g. alkyl halide formation with concentrated hydrohalic acids. Finally, if decomposition is conducted in anhydrous alcohol, ethers may be formed.
So to explicitly answer your questions, 2-diazopropane can produce 1-propene upon decomposition, but it would depend on reaction conditions. Yes, aliphatic diazo compounds generally decompose spontaneously, but some can be held long enough to be synthetically useful. Because of rearrangements and the formation of multiple products, the synthesis of alkenes through a diazo intermediate (by oxidation of hydrazones, for example) would probably not be an advantageous route to access alkenes.
For more information, check out Söll in "Methoden der Organischen Chemie", 4th Edition, Volume 11/2, page 133 (1958).
